EX-1.1

Certain stockholders named in Schedule 1 hereto (the “Selling Stockholders”) of MarketAxess Holdings Inc., a Delaware corporation (the “Company”), propose to sell to J.P. Morgan Securities LLC (the “Underwriter”), an aggregate of 3,597,333 shares of common stock, par value $0.003 per share, of the Company (the “Shares”). The shares of common stock of the Company to be outstanding after giving effect to the sale of the Shares are referred to herein as the “Stock”.

Concurrently with the sale of the Shares, the Company has agreed with the Selling Stockholders to repurchase 1,821,730 shares of non-voting common stock from the Selling Stockholders in a private transaction (the “Share Repurchase”) pursuant to a share repurchase agreement dated February 21, 2012 between the Company and the Selling Stockholders (the “Share Repurchase Agreement”). At the closing of the Share Repurchase, the shares of common stock repurchased by the Company from the Selling Stockholders will be canceled.

The Company and the Selling Stockholders hereby confirm their agreement with the Underwriter concerning the purchase and sale of the Shares, as follows:

1 Registration Statement. The Company has prepared and filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Securities Act”), a registration statement (File No. 333-179601), including a prospectus, relating to the Shares. Such registration statement, as amended at the time it became effective, including the information, if any, deemed pursuant to Rule 430A, 430B or 430C under the Securities Act to be part of the registration statement at the time of its effectiveness (“Rule 430 Information”), is referred to herein as the “Registration Statement”; and as used herein, the term “Preliminary Prospectus” means each prospectus included in such registration statement (and any amendments thereto) before effectiveness, any prospectus filed with the Commission pursuant to Rule 424 under the Securities Act and the prospectus included in the Registration Statement at the time of its effectiveness that omits Rule 430 Information, and the term “Prospectus” means the prospectus in the form first used (or made available upon request of purchasers pursuant to Rule 173 under the Securities Act) in connection with confirmation of sales of the Shares. If the Company has filed an abbreviated registration

statement pursuant to Rule 462(b) under the Securities Act (the “Rule 462 Registration Statement”), then any reference herein to the term “Registration Statement” shall be deemed to include such Rule 462 Registration Statement. Any reference in this Agreement to the Registration Statement, any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include the documents incorporated by reference therein pursuant to Item 12 of Form S-3 under the Securities Act, as of the effective date of the Registration Statement or the date of such Preliminary Prospectus or the Prospectus, as the case may be, and any reference to “amend”, “amendment” or “supplement” with respect to the Registration Statement, any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any documents filed after such date under the Securities Exchange Act of 1934, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Exchange Act”) that are deemed to be incorporated by reference therein. Capitalized terms used but not defined herein shall have the meanings given to such terms in the Registration Statement and the Prospectus.

At or prior to the Applicable Time (as defined below), the Company had prepared the following information (collectively with the pricing information set forth on Annex B, the “Pricing Disclosure Package”): a Preliminary Prospectus dated February 21, 2012, and each “free-writing prospectus” (as defined pursuant to Rule 405 under the Securities Act) listed on Annex B hereto.

“Applicable Time” means 5:45 P.M., New York City time, on February 22, 2012.

(a) Each of the Selling Stockholders agrees, severally and not jointly, to sell the Shares to the Underwriter as provided in this Agreement, and the Underwriter, on the basis of the representations, warranties and agreements set forth herein and subject to the conditions set forth herein, agrees to purchase from each of the Selling Stockholders, the number of Shares as set forth opposite their respective names in Schedule 1 hereto, at a purchase price per share of $28.975 (the “Purchase Price”).

(b) The Selling Stockholders understand that the Underwriter intends to make a public offering of the Shares as soon after the effectiveness of this Agreement as in the judgment of the Underwriter is advisable, and initially to offer the Shares on the terms set forth in the Prospectus. The Selling Stockholders acknowledge and agree that the Underwriter may offer and sell Shares to or through any affiliate of the Underwriter.

(c) Payment for the Shares shall be made by wire transfer in immediately available funds to the account specified by the Selling Stockholders to the Underwriter in the case of the Shares, at the offices of Davis Polk & Wardwell LLP, at 10:00 A.M. New York City time on February 28, 2012, or at such other time or place on the same or such other date, not later than the fifth business day thereafter, as the Underwriter and the Company may agree upon in writing. The time and date of such payment for the Shares is referred to herein as the “Closing Date”.

Payment for the Shares to be purchased on the Closing Date shall be made against delivery to the Underwriter of the Shares to be purchased on such date, with any transfer taxes payable in connection with the sale of such Shares duly paid by the Selling Stockholders. Delivery of the Shares shall be made through the facilities of The Depository Trust Company (the “DTC”) unless the Underwriter shall otherwise instruct. The certificates for the Shares will be made available for inspection and packaging by the Underwriter at the office of DTC or its designated custodian not later than 1:00 P.M., New York City time, on the business day prior to the Closing Date.

(d) Each of the Company and the Selling Stockholders acknowledges and agrees that the Underwriter is acting solely in the capacity of an arm’s length contractual counterparty to the Selling Stockholders with respect to the offering of Shares contemplated hereby (including in connection with determining the terms of the offering) and not as a financial advisor or a fiduciary to, or an agent of, the Company, the Selling Stockholders or any other person. Additionally, the Underwriter is not advising the Company, the Selling Stockholders or any other person as to any legal, tax, investment, accounting or regulatory matters in any jurisdiction. The Company and the Selling Stockholders shall consult with their own advisors concerning such matters and shall be responsible for making their own independent investigation and appraisal of the transactions contemplated hereby, and the Underwriter shall have no responsibility or liability to the Company or the Selling Stockholders with respect thereto. Any review by the Underwriter of the Company, the transactions contemplated hereby or other matters relating to such transactions will be performed solely for the benefit of the Underwriter and shall not be on behalf of the Company or the Selling Stockholders.

3 Representations and Warranties of the Company. The Company represents and warrants to the Underwriter and the Selling Stockholders that:

(a) Preliminary Prospectus. No order preventing or suspending the use of any Preliminary Prospectus has been issued by the Commission, and each Preliminary Prospectus included in the Pricing Disclosure Package, at the time of filing thereof, complied in all material respects with the Securities Act, and no Preliminary Prospectus, at the time of filing thereof, contained any untrue statement of a material fact or omitted to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to the Underwriter furnished to the Company in writing by the Underwriter expressly for use in any Preliminary Prospectus, it being understood and agreed that the only such information furnished by the Underwriter consists of the information described as such in Section 10(c) hereof.

(b) Pricing Disclosure Package. The Pricing Disclosure Package as of the Applicable Time did not, and as of the Closing Date, will not, contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to the Underwriter furnished to the Company in writing by the Underwriter expressly for use in such Pricing Disclosure Package, it being understood and agreed that the only such information furnished by the Underwriter consists of the information described as such in Section 10(c) hereof.

(c) Issuer Free Writing Prospectus. Other than the Registration Statement, the Preliminary Prospectus and the Prospectus, the Company (including its agents and representatives, other than the Underwriter in its capacity as such) has not prepared, used, authorized, approved or referred to and will not prepare, use, authorize, approve or refer to any “written communication” (as defined in Rule 405 under the Securities Act) that constitutes an offer to sell or solicitation of an offer to buy the Shares (each such communication by the Company or its agents and representatives (other than a communication referred to in clause (i) below) an “Issuer Free Writing Prospectus”) other than (i) any document not constituting a prospectus pursuant to Section 2(a)(10)(a) of the Securities Act or Rule 134 under the Securities

Act or (ii) the documents listed on Annex B hereto, each electronic road show and any other written communications approved in writing in advance by the Underwriter. Each such Issuer Free Writing Prospectus complied in all material respects with the Securities Act, has been or will be (within the time period specified in Rule 433) filed in accordance with the Securities Act (to the extent required thereby) and, when taken together with the Preliminary Prospectus filed prior to the first use of such Issuer Free Writing Prospectus, did not, and as of the Closing Date, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in each such Issuer Free Writing Prospectus or Preliminary Prospectus in reliance upon and in conformity with information relating to the Underwriter furnished to the Company in writing by the Underwriter expressly for use in such Issuer Free Writing Prospectus or Preliminary Prospectus, it being understood and agreed that the only such information furnished by the Underwriter consists of the information described as such in Section 10(c) hereof.

(d) Registration Statement and Prospectus. The Registration Statement is an “automatic shelf registration statement” as defined under Rule 405 of the Securities Act that has been filed with the Commission not earlier than three years prior to the date hereof; and no notice of objection of the Commission to the use of such registration statement or any post-effective amendment thereto pursuant to Rule 401(g)(2) under the Securities Act has been received by the Company. No order suspending the effectiveness of the Registration Statement has been issued by the Commission, and no proceeding for that purpose or pursuant to Section 8A of the Securities Act against the Company or related to the offering of the Shares has been initiated or threatened by the Commission; as of the applicable effective date of the Registration Statement and any post-effective amendment thereto, the Registration Statement and any such post-effective amendment complied and will comply in all material respects with the Securities Act, and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; and as of the date of the Prospectus and any amendment or supplement thereto and as of the Closing Date, the Prospectus will not contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to the Underwriter furnished to the Company in writing by the Underwriter expressly for use in the Registration Statement and the Prospectus and any amendment or supplement thereto, it being understood and agreed that the only such information furnished by the Underwriter consists of the information described as such in Section 10(c) hereof.

(e) Incorporated Documents. The documents incorporated by reference in the Registration Statement, the Prospectus and the Pricing Disclosure Package, when they became effective or were filed with the Commission, as the case may be, conformed in all material respects to the requirements of the Securities Act or the Exchange Act, as applicable, and none of such documents contained any untrue statement of a material fact or omitted to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; and any further documents so filed and incorporated by reference in the Registration Statement, the Prospectus or the Pricing Disclosure Package, when such documents become effective or are filed with the Commission, as the case may be, will conform in all material respects to the requirements of the Securities Act or the Exchange Act, as applicable, and will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading.

(f) Financial Statements. The financial statements (including the related notes thereto) of the Company and its consolidated subsidiaries included or incorporated by reference in the Registration Statement, the Pricing Disclosure Package and the Prospectus comply in all material respects with the applicable requirements of the Securities Act and the Exchange Act, as applicable, and present fairly in all material respects the financial position of the Company and its consolidated subsidiaries as of the dates indicated and the results of their operations and the changes in their cash flows for the periods specified; such financial statements have been prepared in conformity with generally accepted accounting principles in the United States applied on a consistent basis throughout the periods covered thereby, and any supporting schedules included or incorporated by reference in the Registration Statement present fairly in all material respects the information required to be stated therein; and the other financial information included or incorporated by reference in the Registration Statement, the Pricing Disclosure Package and the Prospectus has been derived from the accounting records of the Company and its consolidated subsidiaries and presents fairly in all material respects the information shown thereby. The interactive data in eXtensible Business Reporting Language included or incorporated by reference in the Registration Statement, the Pricing Disclosure Package and the Prospectus fairly presents the information called for in all material respects and has been prepared in accordance with the Commission’s rules and guidelines applicable thereto.

(g) No Material Adverse Change. Since the date of the most recent financial statements of the Company included or incorporated by reference in the Registration Statement, the Pricing Disclosure Package and the Prospectus, (i) there has not been any change in the capital stock (other than the issuance of shares of Common Stock upon exercise of stock options and warrants described as outstanding in, and the grant of options and awards under existing equity incentive plans described in, the Registration Statement, the Pricing Disclosure Package and the Prospectus), short-term debt or long-term debt of the Company or any of its subsidiaries, or any dividend or distribution of any kind declared, set aside for payment, paid or made by the Company on any class of capital stock, or any material adverse change, or any development involving a prospective material adverse change, in or affecting the business, properties, management, financial position, stockholders’ equity or results of operations of the Company and its subsidiaries taken as a whole; (ii) neither the Company nor any of its subsidiaries has entered into any transaction or agreement (whether or not in the ordinary course of business) that is material to the Company and its subsidiaries taken as a whole or incurred any liability or obligation, direct or contingent, that is material to the Company and its subsidiaries taken as a whole; and (iii) neither the Company nor any of its subsidiaries has sustained any loss or interference with its business that is material to the Company and its subsidiaries taken as a whole and that is either from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor disturbance or dispute or any action, order or decree of any court or arbitrator or governmental or regulatory authority, except in each case as otherwise disclosed in the Registration Statement, the Pricing Disclosure Package and the Prospectus.

(h) Organization and Good Standing. The Company has been duly incorporated and is an existing corporation in good standing under the laws of the State of Delaware, with power and authority (corporate and other) to own its properties and conduct its business as described in the Prospectus; and the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its

business requires such qualification, except where the failure to so qualify as a foreign corporation would not, individually or in the aggregate, have a material adverse effect on the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole (a “Material Adverse Effect”). Each subsidiary of the Company has been duly incorporated and is an existing corporation in good standing under the laws of the jurisdiction of its incorporation, with power and authority (corporate and other) to own its properties and conduct its business as described in the Prospectus; each subsidiary of the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except where the failure to so qualify as a foreign corporation would not, individually or in the aggregate, have a Material Adverse Effect; the jurisdictions listed on Exhibit A to the opinion to be delivered to the Underwriter by Proskauer Rose LLP pursuant to Section 8(g) hereof and in the opinion to be delivered to the Underwriter by Proskauer Rose LLP pursuant to Section 8(h) hereof are the only jurisdictions in which the Company or any of its subsidiaries maintain an office or lease property.

(i) Capitalization. The outstanding shares of capital stock of the Company (including the Shares to be sold by the Selling Stockholders) have been duly authorized and are validly issued, fully paid and non-assessable and conform to the description thereof in the Registration Statement, Pricing Disclosure Package and the Prospectus, are not subject to any pre-emptive or similar rights.

(j) Due Authorization. The Company has the corporate right, power and authority to execute and deliver this Agreement and the Share Repurchase Agreement (collectively, the “Transaction Documents”) and to perform its obligations hereunder and thereunder; and all corporate action required to be taken for the due and proper authorization, execution and delivery by it of this Agreement and the Share Repurchase Agreement and the consummation by it of the transactions contemplated hereby and thereby has been duly and validly taken.

(k) Underwriting Agreement and Share Repurchase Agreement. This Agreement has been duly authorized, executed and delivered by the Company. The Share Repurchase Agreement has been duly authorized, executed and delivered by the Company and constitutes a valid and legally binding agreement of the Company enforceable against the Company in accordance with its terms, except as enforceability may be limited by applicable bankruptcy, insolvency or similar laws affecting creditors’ rights generally or by equitable principles relating to enforceability.

(l) No Conflicts. The execution, delivery and performance of the Transaction Documents, and the consummation of the transactions contemplated therein will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, any statute, any rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any subsidiary of the Company or any of their properties, or any material agreement or instrument to which the Company or any such subsidiary is a party or by which the Company or any such subsidiary is bound or to which any of the properties of the Company or any such subsidiary is subject, or the charter or bylaws of the Company or any such subsidiary.

(m) No Consents Required. No consent, approval, authorization, or order of, or filing with, any governmental agency or body or any court is required to be obtained or made by the Company for the consummation of the transactions contemplated by the Transaction Documents

in connection with the sale of the Shares, except such as have been obtained and made under the Securities Act or under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), such as have been obtained from NASDAQ, and such as may be required under state securities laws.

(n) Legal Proceedings. Except as described in the Registration Statement, the Pricing Disclosure Package and the Prospectus, there are no pending actions, suits or proceedings against or affecting the Company, any of its subsidiaries or any of their respective properties that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect, or would materially and adversely affect the ability of the Company to perform its obligations under this Agreement, or which are otherwise material in the context of the sale of the Shares; and no such actions, suits or proceedings, to the Company’s knowledge, have been threatened or are currently contemplated.

(o) Independent Accountants. PricewaterhouseCoopers LLP, who have certified certain financial statements of the Company and its subsidiaries and is an independent registered public accounting firm with respect to the Company and its subsidiaries within the applicable rules and regulations adopted by the Commission and the Public Company Accounting Oversight Board (United States) and as required by the Securities Act.

(p) Title to Real and Personal Property. Except as disclosed in the Registration Statement, the Pricing Disclosure Package and the Prospectus, the Company and its subsidiaries have good and marketable title to all real properties and all other properties and assets owned by them, in each case free from liens, encumbrances and defects that would materially affect the value thereof or materially interfere with the use made or to be made thereof by them; and except as disclosed in the Registration Statement, the Pricing Disclosure Package and the Prospectus, the Company and its subsidiaries hold any leased real or personal property under valid and enforceable leases with no exceptions that would materially interfere with the use made or to be made thereof by them.

(q) Title to Intellectual Property. The Company and its subsidiaries own, possess the right to use or can acquire the right to use on reasonable terms, adequate trademarks, trade names and other rights to those inventions, know-how, patents, copyrights, confidential information and other intellectual property (collectively, the “intellectual property rights”) necessary to conduct the business now operated by them, or presently employed by them, and have not received any written notice of infringement with respect to any third party intellectual property rights that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(r) Investment Company Act. The Company is not and, after giving effect to the offering and sale of the Shares and the application of the proceeds thereof as described in the Registration Statement, the Pricing Disclosure Package and the Prospectus, will not be required to register as an “investment company” or an entity “controlled” by an “investment company” within the meaning of the Investment Company Act of 1940, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Investment Company Act”).

(s) Permits. The Company and its subsidiaries possess adequate certificates, authorities or permits issued by appropriate governmental agencies or bodies necessary to conduct the business now operated by them and have not received any notice of proceedings relating to the revocation or modification of any such certificate, authority or permit that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(t) No Labor Disputes. No labor dispute with the employees of the Company or any subsidiary exists or, to the knowledge of the Company, is imminent that might have a Material Adverse Effect.

(u) Compliance with and Liability Under Environmental Laws. Except as disclosed in the Registration Statement, the Pricing Disclosure Package and the Prospectus, neither the Company nor any of its subsidiaries is in violation of any statute, any rule, regulation, decision or order of any governmental agency or body or any court, domestic or foreign, relating to the use, disposal or release of hazardous or toxic substances or relating to the protection or restoration of the environment or human exposure to hazardous or toxic substances (collectively, the “environmental laws”), owns or operates any real property contaminated with any substance that is subject to any environmental laws, is liable for any off-site disposal or contamination pursuant to any environmental laws, or is subject to any claim relating to any environmental laws, which violation, contamination, liability or claim would individually or in the aggregate have a Material Adverse Effect; and the Company is not aware of any pending investigation which might lead to such a claim.

(v) Disclosure Controls. The Company maintains an effective system of “disclosure controls and procedures” (as such term is defined in Rule 13a-15(e) under the Exchange Act) that complies with the requirements of the Exchange Act and that has been designed to ensure that information required to be disclosed by the Company in the reports that it files or submits under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the Commission’s rules and forms, including controls and procedures designed to ensure that such information is accumulated and communicated to the Company’s management as appropriate to allow timely decisions regarding required disclosure. The Company and its subsidiaries have carried out evaluations of the effectiveness of their disclosure controls and procedures as required by Rule 13a-15 of the Exchange Act.

(w) Accounting Controls. Each of the Company and its subsidiaries maintain systems of “internal control over financial reporting” (as defined in Rule 13a-15(f) of the Exchange Act) that comply with the requirements of the Exchange Act and have been designed by, or under the supervision of, their respective principal executive and principal financial officers, or persons performing similar functions, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles, including, but not limited to, internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences; and (v) the interactive data in eXtensible Business Reporting Language incorporated by reference in the Registration Statement, the Pricing Disclosure Package and the Prospectus fairly presents the information called for in all material respects and is prepared in accordance with the Commission’s rules and guidelines applicable thereto. Except as disclosed in the Registration Statement, the Pricing Disclosure Package and the Prospectus, there are no material weaknesses in the Company’s internal controls. The

Company’s auditors and the Audit Committee of the Board of Directors of the Company have been advised of: (i) all significant deficiencies and material weaknesses in the design or operation of internal controls over financial reporting which have adversely affected or are reasonably likely to adversely affect the Company’s ability to record, process, summarize and report financial information; and (ii) any fraud, whether or not material, that involves management or other employees who have a significant role in the Company’s internal controls over financial reporting.

(x) No Unlawful Payments. Neither the Company nor any of its subsidiaries nor, to the knowledge of the Company, any director, officer, agent, employee or other person associated with or acting on behalf of the Company or any of its subsidiaries has (i) used any corporate funds for any unlawful contribution, gift, entertainment or other unlawful expense relating to political activity; (ii) made any direct or indirect unlawful payment to any foreign or domestic government official or employee from corporate funds; (iii) violated or is in violation of any provision of the Foreign Corrupt Practices Act of 1977; or (iv) made any bribe, rebate, payoff, influence payment, kickback or other unlawful payment.

(y) Compliance with Money Laundering Laws. The operations of the Company and its subsidiaries are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, the money laundering statutes of all jurisdictions, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Money Laundering Laws”), in each case, to the extent applicable to the Company and its subsidiaries, and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or any of its subsidiaries with respect to the Money Laundering Laws is pending or, to the knowledge of the Company, threatened.

(z) Compliance with OFAC. None of the Company, any of its subsidiaries or, to the knowledge of the Company, any director, officer, agent, employee or affiliate of the Company or any of its subsidiaries is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Department of the Treasury.

(aa) No Broker’s Fees. Except as disclosed in the Registration Statement, the Pricing Disclosure Package and the Prospectus, there are no contracts, agreements or understandings between the Company and any person that would give rise to a valid claim against the Company or any Underwriter for a brokerage commission, finder’s fee or other like payment in connection with this offering.

(bb) No Registration Rights. Except as described in the Registration Statement, the Pricing Disclosure Package and the Prospectus, there are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Securities Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to a Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act.

(cc) No Stabilization. The Company has not taken, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

(dd) Forward-Looking Statements. No forward-looking statement (within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act) contained in the Registration Statement, the Pricing Disclosure Package or the Prospectus has been made or reaffirmed without a reasonable basis or has been disclosed other than in good faith.

(ee) Statistical and Market Data. Any statistical and market-related data included in the Registration Statement, the Pricing Disclosure Package and the Prospectus are based on or derived from sources that the Company believes to be reliable and accurate, and the Company has obtained the written consent to the use of such data from such sources to the extent required.

(ff) Sarbanes-Oxley Act. There is and has been no failure on the part of the Company or, to the knowledge of the Company, any of the Company’s directors or officers, in their capacities as such, to comply with any provision of the Sarbanes-Oxley Act of 2002 and the rules and regulations promulgated in connection therewith, including Section 402 related to loans and Sections 302 and 906 related to certifications.

(gg) Status Under the Securities Act. At the time of filing the Registration Statement and any post-effective amendment thereto, at the earliest time thereafter that any offering participant made a bona fide offer (within the meaning of Rule 164(h)(2) under the Securities Act) of the Shares and at the date hereof, the Company was not and is not an “ineligible issuer”, and is a well-known seasoned issuer, in each case as defined in Rule 405 under the Securities Act. The Company has paid the registration fee for this offering pursuant to Rule 456(b)(1) under the Securities Act or will pay such fee within the time period required by such rule (without giving effect to the proviso therein) and in any event prior to the Closing Date.

(hh) No Ratings. There are no securities or preferred stock of or guaranteed by the Company or any of its subsidiaries that are rated by a “nationally recognized statistical rating organization”, as such term is defined in Section 3(a)(62) of the Exchange Act.

(ii) Registered Broker-dealer. MarketAxess Corporation is registered under the Exchange Act as a broker-dealer and is a member in good standing of the Financial Industry Regulatory Authority, and neither the Company nor any other subsidiary is required to be so registered; MarketAxess Europe Limited is registered with the Financial Services Authority as a dealer and is a member in good standing of the Financial Services Authority and neither the Company nor any other subsidiary is required to be so registered; MarketAxess Canada Ltd. is registered with the Ontario Securities Commission as a registered Alternative Trading System dealer and is a member in good standing of the Investment Industry Regulatory Organization of Canada and neither the Company nor any other subsidiary is required to be so registered; and to the extent required in connection with their respective businesses, each of the Company and its subsidiaries is also registered as a broker-dealer in each state or other jurisdiction in which the failure to so register would have a Material Adverse Effect.

4 Representations and Warranties of the Selling Stockholders. Each of the Selling Stockholders represents and warrants to the Underwriter and the Company that:

(a) Required Consents; Authority. All consents, approvals, authorizations and orders necessary for the execution and delivery by such Selling Stockholder of the Transaction Documents, and for the sale and delivery of the Shares to be sold by such Selling Stockholder thereunder, have been obtained; and such Selling Stockholder has full right, power and authority to enter into the Transaction Documents and to sell, assign, transfer and deliver the Shares to be sold by such Selling Stockholder thereunder; each of the Transaction Documents has been duly authorized, executed and delivered by such Selling Stockholder.

(b) No Conflicts. The execution, delivery and performance of the Transaction Documents, and the consummation of the transactions therein contemplated will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, any statute, any rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over such Selling Stockholder or any of its properties, or any material agreement or instrument to which such Selling Stockholder is a party or by which such Selling Stockholder is bound or to which any of the properties of such Selling Stockholder is subject, or the charter or bylaws of such Selling Stockholder.

(c) Title to Shares. Such Selling Stockholder has good and valid title to the Shares to be sold at the Closing Date, by such Selling Stockholder hereunder, free and clear of all liens, encumbrances, equities or adverse claims and such Selling Stockholder will have, immediately prior to the Closing Date, good and valid title to the Shares to be sold at the Closing Date, by such Selling Stockholder hereunder, free and clear of all liens, encumbrances, equities or adverse claims; and, upon delivery of the certificates representing such Shares and payment therefor pursuant hereto, good and valid title to such Shares, free and clear of all liens, encumbrances, equities or adverse claims, will pass to the Underwriter.

(d) No Stabilization. Such Selling Stockholder has not taken and will not take, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

(e) Pricing Disclosure Package. The Pricing Disclosure Package, at the Applicable Time did not, and at the Closing Date, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that such Selling Stockholder’s representation under this Section 4(e) shall only apply to any untrue statement of a material fact or omission to state a material fact made in reliance upon and in conformity with any information relating to such Selling Stockholder furnished to the Company in writing by such Selling Stockholder expressly for use in the Pricing Disclosure Package.

(f) Issuer Free Writing Prospectus. Other than the Registration Statement, the Preliminary Prospectus and the Prospectus, such Selling Stockholder (including its agents and representatives, other than the Underwriter in its capacity as such) has not made, used, prepared, authorized, approved or referred to and will not prepare, make, use, authorize, approve or refer to any Issuer Free Writing Prospectus, other than (i) any document not constituting a prospectus pursuant to Section 2(a)(10)(a) of the Securities Act or Rule 134 under the Securities Act or (ii) the documents listed on Annex B hereto, each electronic road show and any other written communications approved in writing in advance by the Company and the Underwriter.

(g) Registration Statement and Prospectus. As of the applicable effective date of the Registration Statement and any post-effective amendment thereto, the Registration Statement and any such post-effective amendment complied and will comply in all material respects with the Securities Act, and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; and as of the date of the Prospectus and any amendment or supplement thereto and as of the Closing Date, the Prospectus will not contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that such Selling Stockholder’s representation under this Section 4(g) shall only apply to any untrue statement of a material fact or omission to state a material fact made in reliance upon and in conformity with any information relating to such Selling Stockholder furnished to the Company in writing by such Selling Stockholder expressly for use in the Registration Statement or the Prospectus (or any amendment or supplement thereto).

(h) Material Information. As of the date hereof, as of the Closing Date, that the sale of the Shares by such Selling Stockholder is not and will not be prompted by any material information concerning the Company which is not set forth in the Registration Statement, the Pricing Disclosure Package or the Prospectus.

5 Further Agreements of the Company. The Company covenants and agrees with the Underwriter that:

(a) Required Filings. The Company will file the final Prospectus with the Commission within the time periods specified by Rule 424(b) and Rule 430A, 430B or 430C under the Securities Act, will file any Issuer Free Writing Prospectus to the extent required by Rule 433 under the Securities Act; will file promptly all reports and any definitive proxy or information statements required to be filed by the Company with the Commission pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of the Prospectus and for so long as the delivery of a prospectus is required in connection with the offering or sale of the Shares; and will furnish copies of the Prospectus and each Issuer Free Writing Prospectus (to the extent not previously delivered) to the Underwriter in New York City prior to 10:00 A.M., New York City time, on the second business day next succeeding the date of this Agreement in such quantities as the Underwriter may reasonably request. The Company will pay the registration fee for this offering within the time period required by Rule 456(b)(1) under the Securities Act (without giving effect to the proviso therein) and in any event prior to the Closing Date.

(b) Delivery of Copies. To the extent not available on the Commission’s EDGAR system or any successor system, the Company will deliver, without charge, to the Underwriter, (i) two signed copies of the Registration Statement as originally filed and each amendment thereto, in each case including all exhibits and consents filed therewith; and (ii) during the Prospectus Delivery Period (as defined below), as many copies of the Prospectus (including all amendments and supplements thereto and each Issuer Free Writing Prospectus) as the Underwriter may reasonably request. As used herein, the term “Prospectus Delivery Period” means such period of time after the first date of the public offering of the Shares as in the opinion of counsel for the Underwriter a prospectus relating to the Shares is required by law to be delivered (or required to be delivered but for Rule 172 under the Securities Act) in connection with sales of the Shares by the Underwriter or dealer.

(c) Amendments or Supplements, Issuer Free Writing Prospectuses. Before making, preparing, using, authorizing, approving, referring to or filing any Issuer Free Writing Prospectus, and before filing any amendment or supplement to the Registration Statement or the Prospectus, whether before or after the time that the Registration Statement becomes effective, the Company will furnish to the Underwriter and counsel for the Underwriter a copy of the proposed Issuer Free Writing Prospectus, amendment or supplement for review and will not prepare, use, authorize, approve, refer to or file any such Issuer Free Writing Prospectus or file any such proposed amendment or supplement to which the Underwriter reasonably and timely objects.

(d) Notice to the Underwriter. The Company will advise the Underwriter promptly, and confirm such advice in writing, (i) when any amendment to the Registration Statement has been filed or becomes effective; (ii) when any supplement to the Prospectus or any Issuer Free Writing Prospectus or any amendment to the Prospectus has been filed; (iii) of any request by the Commission for any amendment to the Registration Statement or any amendment or supplement to the Prospectus or the receipt of any comments from the Commission relating to the Registration Statement or any other request by the Commission for any additional information; (iv) of the issuance by the Commission of any order suspending the effectiveness of the Registration Statement or preventing or suspending the use of any Preliminary Prospectus, any of the Pricing Disclosure Package or the Prospectus or the initiation or threatening of any proceeding for that purpose or pursuant to Section 8A of the Securities Act; (v) of the occurrence of any event within the Prospectus Delivery Period as a result of which the Prospectus, the Pricing Disclosure Package or any Issuer Free Writing Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances existing when the Prospectus, the Pricing Disclosure Package or any such Issuer Free Writing Prospectus is delivered to a purchaser, not misleading; (vi) of the receipt by the Company of any notice of objection of the Commission to the use of the Registration Statement or any post-effective amendment thereto pursuant to Rule 401(g)(2) under the Securities Act; and (vii) of the receipt by the Company of any notice with respect to any suspension of the qualification of the Shares for offer and sale in any jurisdiction or the initiation or threatening of any proceeding for such purpose; and the Company will use its best efforts to prevent the issuance of any such order suspending the effectiveness of the Registration Statement, preventing or suspending the use of any Preliminary Prospectus, any of the Pricing Disclosure Package or the Prospectus or suspending any such qualification of the Shares and, if any such order is issued, will obtain as soon as possible the withdrawal thereof.

(e) Ongoing Compliance. (1) If during the Prospectus Delivery Period (i) any event shall occur or condition shall exist as a result of which the Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances existing when the Prospectus is delivered to a purchaser, not misleading or (ii) it is necessary to amend or supplement the Prospectus to comply with law, the Company will promptly notify the Underwriter thereof and forthwith prepare and, subject to paragraph (c) above, file with the Commission and furnish to the Underwriter and to such dealers as the Underwriter may designate such amendments or supplements to the Prospectus as may be necessary so that the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances existing when the Prospectus is delivered to a purchaser, be misleading or so that the Prospectus will comply with law and (2) if at any time prior to the Closing Date (i) any event shall occur or condition shall exist as a result of which the Pricing Disclosure Package as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances existing when the Pricing Disclosure Package is delivered to a purchaser, not misleading or (ii) it is

necessary to amend or supplement the Pricing Disclosure Package to comply with law, the Company will promptly notify the Underwriter thereof and forthwith prepare and, subject to paragraph (c) above, file with the Commission (to the extent required) and furnish to the Underwriter and to such dealers as the Underwriter may designate, such amendments or supplements to the Pricing Disclosure Package as may be necessary so that the statements in the Pricing Disclosure Package as so amended or supplemented will not, in the light of the circumstances existing when the Pricing Disclosure Package is delivered to a purchaser, be misleading or so that the Pricing Disclosure Package will comply with law.

(f) Earning Statement. The Company will make generally available to its security holders and the Underwriter as soon as practicable an earning statement that satisfies the provisions of Section 11(a) of the Securities Act and Rule 158 of the Commission promulgated thereunder covering a period of at least twelve months beginning with the first fiscal quarter of the Company occurring after the “effective date” (as defined in Rule 158) of the Registration Statement.

(g) Clear Market. For a period of 90 days after the date of the Prospectus, the Company will not (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, or file with the Commission a registration statement under the Securities Act relating to, any shares of Stock or any securities convertible into or exercisable or exchangeable for Stock, or publicly disclose the intention to make any offer, sale, pledge, disposition or filing, or (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Stock or any such other securities, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Stock or such other securities, in cash or otherwise, without the prior written consent of the Underwriter, other than the (A) Shares to be sold hereunder, (B) stock options granted pursuant to existing stock-based compensation plans of the Company and its subsidiaries (the “Company Stock Plans”) or any shares of Stock of the Company issued upon the exercise of options granted under Company Stock Plans or (C) shares of Stock of the Company issued in connection with a transaction with an unaffiliated third party that includes a bona fide commercial relationship with the Company (including joint ventures, marketing or distribution arrangements, collaboration agreements or intellectual property license agreements), provided that prior to the issuance of any shares of Stock pursuant to this clause (C) during the 90-day restricted period, the recipient of such shares of Stock shall sign and deliver a lock-up agreement substantially in the form of Exhibit A hereto and the aggregate amount of shares of Common Stock issued pursuant to this clause (C) does not exceed 5% of the outstanding shares of Common Stock of the Company.

(h) No Stabilization. The Company will not take, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Stock.

(i) Reports. So long as the Shares are outstanding, the Company will furnish to the Underwriter, as soon as they are available, copies of all reports or other communications (financial or other) furnished to holders of the Shares, and copies of any reports and financial statements furnished to or filed with the Commission or any national securities exchange or automatic quotation system; provided the Company will be deemed to have furnished such reports and financial statements to the Underwriter to the extent they are filed on the Commission’s Electronic Data Gathering, Analysis, and Retrieval system.

(j) Record Retention. The Company will, pursuant to reasonable procedures developed in good faith, retain copies of each Issuer Free Writing Prospectus that is not filed with the Commission in accordance with Rule 433 under the Securities Act.

6 Further Agreements of the Selling Stockholders. Each of the Selling Stockholders covenants and agrees with the Underwriter that:

(a) Tax Form. It will deliver to the Underwriter prior to or at the Closing Date a properly completed and executed United States Treasury Department Form W-9 (or other applicable form or statement specified by the Treasury Department regulations in lieu thereof) in order to facilitate the Underwriter’s documentation of their compliance with the reporting and withholding provisions of the Tax Equity and Fiscal Responsibility Act of 1982 with respect to the transactions herein contemplated.

(b) Conversion Notice and Share Transfer. In connection with the sale of the Shares, LabMorgan Corporation shall deliver or transfer, as applicable, (i) an executed notice of conversion (“Conversion Notice”) and (ii) the 763,924 shares of non-voting common stock to be converted, to the Company, in each case within one business day after the date of this Agreement.

7 Certain Agreements of the Underwriter. The Underwriter hereby represents and agrees that:

(a) It has not used, authorized use of, referred to or participated in the planning for use of, and will not use, authorize use of, refer to, or participate in the planning for use of, any “free writing prospectus”, as defined in Rule 405 under the Securities Act (which term includes use of any written information furnished to the Commission by the Company and not incorporated by reference into the Registration Statement and any press release issued by the Company) other than (i) a free writing prospectus that contains no “issuer information” (as defined in Rule 433(h)(2) under the Securities Act) that was not included (including through incorporation by reference) in the Preliminary Prospectus or a previously filed Issuer Free Writing Prospectus, (ii) any Issuer Free Writing Prospectus listed on Annex B or prepared pursuant to Section 3(c) or Section 4(c) above (including any electronic road show), or (iii) any free writing prospectus prepared by the underwriter and approved by the Company in advance in writing (each such free writing prospectus referred to in clauses (i) or (iii), an “Underwriter Free Writing Prospectus”).

(b) It is not subject to any pending proceeding under Section 8A of the Securities Act with respect to the offering (and will promptly notify the Company if any such proceeding against it is initiated during the Prospectus Delivery Period).

8 Conditions of Underwriter’s Obligations. The obligation of the Underwriter to purchase the Shares on the Closing Date, as provided herein is subject to the performance by the Company and each of the Selling Stockholders of their respective covenants and other obligations hereunder and to the following additional conditions:

(a) Registration Compliance; No Stop Order. No order suspending the effectiveness of the Registration Statement shall be in effect, and no proceeding for such purpose , pursuant to Rule 401(g)(2) or pursuant to Section 8A under the Securities Act shall be pending before or threatened by the Commission; the Prospectus and each Issuer Free Writing Prospectus shall have been timely filed with the Commission under the Securities Act (in the case of an Issuer Free Writing Prospectus, to the extent required by Rule 433 under the Securities Act) and in accordance with Section 5(a) hereof; and all requests by the Commission for additional information shall have been complied with to the reasonable satisfaction of the Underwriter.

(b) Representations and Warranties. The respective representations and warranties of the Company and the Selling Stockholders contained herein shall be true and correct on the date hereof and on and as of the Closing Date, and the statements of the Company and its officers and of each of the Selling Stockholders made in any certificates delivered pursuant to this Agreement shall be true and correct on and as of the Closing Date.

(c) No Material Adverse Change. No event or condition of a type described in Section 3(g) hereof shall have occurred or shall exist, which event or condition is not described in the Pricing Disclosure Package (excluding any amendment or supplement thereto) and the Prospectus (excluding any amendment or supplement thereto) and the effect of which in the judgment of the Underwriter makes it impracticable or inadvisable to proceed with the offering, sale or delivery of the Shares on the Closing Date, on the terms and in the manner contemplated by this Agreement, the Pricing Disclosure Package and the Prospectus.

(d) Officer’s Certificate and Selling Stockholders’ Certificates. The Underwriter shall have received on and as of the Closing Date, a certificate of (i) the chief financial officer or chief accounting officer of the Company and one additional senior executive officer of the Company who is satisfactory to the Underwriter (A) confirming that the representations and warranties of the Company in this Agreement are true and correct, (B) the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to such Closing Date; and (C) to the Company’s knowledge, no stop order suspending the effectiveness of any Registration Statement has been issued and no proceedings for that purpose have been instituted or are contemplated by the Commission and (ii) each of the Selling Stockholders, in form and substance reasonably satisfactory to the Underwriter, (A) confirming that the representations of the Selling Stockholders set forth in Sections 4(e), 4(f) and 4(g) hereof is true and correct and (B) confirming that the other representations and warranties of the Selling Stockholders in this agreement are true and correct and that the Selling Stockholders have complied with all agreements and satisfied all conditions on their part to be performed or satisfied hereunder at or prior to such Closing Date.

(e) Comfort Letters. On the date of this Agreement and on the Closing Date, PricewaterhouseCoopers LLP shall have furnished to the Underwriter, at the request of the Company, letters, dated the respective dates of delivery thereof and addressed to the Underwriter, in form and substance reasonably satisfactory to the Underwriter, containing statements and information of the type customarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained or incorporated by reference in the Registration Statement, the Pricing Disclosure Package and the Prospectus; provided, that the letter delivered on the Closing Date, shall use a “cut-off” date no more than three business days prior to such Closing Date.

(f) Opinion and 10b-5 Statement of Counsel for the Company. Proskauer Rose LLP, counsel for the Company, shall have furnished to the Underwriter, at the request of the Company, their written opinion and 10b-5 statement, dated the Closing Date, and addressed to the Underwriter, in form and substance reasonably satisfactory to the Underwriter, to the effect set forth in Annex A-1(a) and (b) hereto.

(g) Opinion of UK Counsel for the Company. Proskauer Rose LLP, United Kingdom counsel for the Company, shall have furnished to the Underwriter, at the request of the Company, their written opinion, dated the Closing Date, and addressed to the Underwriter, in form and substance reasonably satisfactory to the Underwriter, to the effect set forth in Annex A-2 hereto.

(h) Opinion and 10b-5 Statement of Counsel for the Underwriter. The Underwriter shall have received on and as of the Closing Date, an opinion and 10b-5 statement of Davis Polk & Wardwell LLP, counsel for the Underwriter, with respect to such matters as the Underwriter may reasonably request, and such counsel shall have received such documents and information as they may reasonably request to enable them to pass upon such matters.

(i) No Legal Impediment to Sale. No action shall have been taken and no statute, rule, regulation or order shall have been enacted, adopted or issued by any federal, state or foreign governmental or regulatory authority that would, as of the Closing Date, prevent the sale of the Shares; and no injunction or order of any federal, state or foreign court shall have been issued that would, as of the Closing Date, prevent the sale of the Shares.

(j) Good Standing. The Underwriter shall have received on and as of the Closing Date, satisfactory evidence of the good standing of the Company and its subsidiaries in their respective jurisdictions of organization and their good standing as foreign entities in such other jurisdictions as the Underwriter may reasonably request, in each case in writing or any standard form of telecommunication from the appropriate governmental authorities of such jurisdictions.

(k) Exchange Listing. The Shares to be delivered on the Closing Date shall have been approved for listing on NASDAQ.

(l) Lock-up Agreements. The “lock-up” agreements, each substantially in the form of Exhibit A hereto, between the Underwriter and certain officers and directors of the Company relating to sales and certain other dispositions of shares of Stock or certain other securities, delivered to the Underwriter on or before the date hereof, shall be full force and effect on the Closing Date.

(m) Conversion Notice and Share Transfer. LabMorgan Corporation shall have delivered the Conversion Notice and transferred the related shares as provided under Section 6(b) of this Agreement.

(n) Additional Documents. On or prior to the Closing Date, the Company and the Selling Stockholders shall have furnished to the Underwriter such further certificates and documents as the Underwriter may reasonably request.

All opinions, letters, certificates and evidence mentioned above or elsewhere in this Agreement shall be deemed to be in compliance with the provisions hereof only if they are in form and substance reasonably satisfactory to counsel for the Underwriter.

9 Conditions of the Company’s Obligations. The performance of the Company’s obligations on the Closing Date as provided herein is contingent on the consummation of the transactions contemplated by the Share Repurchase Agreement pursuant to the terms thereof.

(a) Indemnification of the Underwriter by the Company. The Company agrees to indemnify and hold harmless the Underwriter, its affiliates, directors and officers and each person, if any, who controls the Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act, from and against any and all losses, claims, damages and liabilities (including, without limitation, reasonable legal fees and other expenses incurred in connection with any suit, action or proceeding or any claim asserted, as such fees and expenses are incurred), joint or several, that arise out of, or are based upon, (i) any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or caused by any omission or alleged omission to state therein a material fact required to be stated therein or necessary in order to make the statements therein, not misleading, (ii) or any untrue statement or alleged untrue statement of a material fact contained in the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus, any “issuer information” filed or required to be filed pursuant to Rule 433(d) under the Securities Act, any road show as defined in Rule 433(h) under the Securities Act (a “road show”) or any Pricing Disclosure Package, or caused by any omission or alleged omission to state therein a material fact necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading, in each case except insofar as such losses, claims, damages or liabilities arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to the Underwriter furnished to the Company in writing by the Underwriter for use therein, it being understood and agreed that the only such information furnished by the Underwriter consists of the information described as such in subsection (c) below.

(b) Indemnification of the Underwriter by the Selling Stockholders. Each of the Selling Stockholders, severally in proportion to the number of Shares to be sold by such Selling Stockholder hereunder, agrees to indemnify and hold harmless the Underwriter, its affiliates, directors and officers and each person, if any, who controls the Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the indemnity set forth in paragraph (a) above; provided, however, that (i) such Selling Stockholder’s agreement to indemnify and hold harmless hereunder shall only apply insofar as such losses, claims, damages or liabilities arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to such Selling Stockholder furnished to the Company in writing by such Selling Stockholder expressly for use in the Registration Statement, the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus or any Pricing Disclosure Package, and (ii) the aggregate amount of the Selling Shareholder’s liability pursuant to this Section 10(b) shall not exceed the aggregate amount of gross proceeds net of underwriting discount received by such Selling Stockholder from the sale of its Shares hereunder.

(c) Indemnification of the Company and the Selling Stockholders. The Underwriter agrees, severally and not jointly, to indemnify and hold harmless the Company, its directors, its officers who signed the Registration Statement and each person, if any, who controls the Company within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act and each of the Selling Stockholders to the same extent as the indemnity set forth in paragraph (a) above, but only with respect to any losses, claims, damages or liabilities that arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to the Underwriter furnished to the Company in writing by the Underwriter expressly for use in the Registration Statement, the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus, any road show or any Pricing Disclosure Package (including any Pricing Disclosure Package that has subsequently been amended), it being understood and agreed upon that the only such information furnished by the Underwriter consists of the following information in the Prospectus furnished on behalf of the Underwriter: the concession figure appearing in the third paragraph under the caption “Underwriting.”

(d) Notice and Procedures. If any suit, action, proceeding (including any governmental or regulatory investigation), claim or demand shall be brought or asserted against any person in respect of which indemnification may be sought pursuant to the preceding paragraphs of this Section 10, such person (the “Indemnified Person”) shall promptly notify the person against whom such indemnification may be sought (the “Indemnifying Person”) in writing; provided that the failure to notify the Indemnifying Person shall not relieve it from any liability that it may have under the preceding paragraphs of this Section 10 except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided, further, that the failure to notify the Indemnifying Person shall not relieve it from any liability that it may have to an Indemnified Person otherwise than under the preceding paragraphs of this Section 10. If any such proceeding shall be brought or asserted against an Indemnified Person and it shall have notified the Indemnifying Person thereof, the Indemnifying Person shall retain counsel reasonably satisfactory to the Indemnified Person (who shall not, without the consent of the Indemnified Person, be counsel to the Indemnifying Person) to represent the Indemnified Person in such proceeding and shall pay the reasonable fees and expenses of such counsel related to such proceeding, as incurred. In any such proceeding, any Indemnified Person shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such Indemnified Person unless (i) the Indemnifying Person and the Indemnified Person shall have mutually agreed to the contrary; (ii) the Indemnifying Person has failed within a reasonable time to retain counsel reasonably satisfactory to the Indemnified Person; (iii) the Indemnified Person shall have reasonably concluded that there may be legal defenses available to it that are different from or in addition to those available to the Indemnifying Person; or (iv) the named parties in any such proceeding (including any impleaded parties) include both the Indemnifying Person and the Indemnified Person and representation of both parties by the same counsel would be inappropriate due to actual or potential differing interest between them. It is understood and agreed that the Indemnifying Person shall not, in connection with any proceeding or related proceedings in the same jurisdiction, be liable for the fees and expenses of more than one separate firm (in addition to any local counsel) for all Indemnified Persons, and that all such fees and expenses shall be paid or reimbursed as they are incurred. Any such separate firm for the Underwriter, its affiliates, directors and officers and any control persons of the Underwriter shall be designated in writing by the Underwriter, and any such separate firm for the Company, its directors, its officers who signed the Registration Statement and any control persons of the Company shall be designated in writing by the Company and any such separate firm for the Selling Stockholders shall be designated in writing by the Selling Stockholders. The Indemnifying Person shall not be liable for any settlement of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff, the Indemnifying Person agrees to indemnify each Indemnified Person from and against any loss or liability by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an Indemnified Person shall have requested that an Indemnifying Person reimburse the Indemnified Person for fees and expenses of counsel as contemplated by this paragraph, the Indemnifying Person shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than 30 days after receipt by the Indemnifying Person of such request and (ii) the Indemnifying Person shall not have reimbursed the Indemnified Person in accordance with such request prior to the date of such settlement. No Indemnifying Person shall, without the written consent of the Indemnified Person, effect any settlement of any pending or threatened proceeding in respect of which any Indemnified Person is or could have been a party and indemnification could have been sought hereunder by such Indemnified Person, unless such settlement (x) includes an unconditional release of such Indemnified Person, in form and substance reasonably satisfactory to such Indemnified Person, from all liability on claims that are the subject matter of such proceeding and (y) does not include any statement as to or any admission of fault, culpability or a failure to act by or on behalf of any Indemnified Person.

(e) Contribution. If the indemnification provided for in paragraphs (a), (b) and (c) above is unavailable to an Indemnified Person or insufficient in respect of any losses, claims, damages or liabilities referred to therein, then each Indemnifying Person under such paragraph, in lieu of indemnifying such Indemnified Person thereunder, shall contribute to the amount paid or payable by such Indemnified Person as a result of such losses, claims, damages or liabilities (i) in such proportion as is appropriate to reflect the relative benefits received by the Company and the Selling Stockholders, on the one hand, and the Underwriter on the other, from the offering of the Shares or (ii) if the allocation provided by clause (i) is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) but also the relative fault of the Company and the Selling Stockholders, on the one hand, and the Underwriter on the other, in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant equitable considerations. The relative benefits received by the Company and the Selling Stockholders, on the one hand, and the Underwriter on the other, shall be deemed to be in the same respective proportions as the net proceeds (before deducting expenses) received by the Selling Stockholders from the sale of the Shares and the total underwriting discounts and commissions received by the Underwriter in connection therewith, in each case as set forth in the table on the cover of the Prospectus, bear to the aggregate offering price of the Shares. The relative fault of the Company and the Selling Stockholders, on the one hand, and the Underwriter on the other, shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company and the Selling Stockholders or by the Underwriter and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

(f) Limitation on Liability. The Company, the Selling Stockholders and the Underwriter agree that it would not be just and equitable if contribution pursuant to this Section 10 were determined by pro rata allocation (even if the Selling Stockholders or the Underwriter were treated as one entity for such purpose) or by any other method of allocation that does not take account of the equitable considerations referred to in paragraph (e) above. The amount paid or payable by an Indemnified Person as a result of the losses, claims, damages and liabilities referred to in paragraph (e) above shall be deemed to include, subject to the limitations set forth above, any legal or other expenses incurred by such Indemnified Person in connection with any such action or claim. Notwithstanding the provisions of this Section 10, in no event shall an Underwriter be required to contribute any amount in excess of the amount by which the total underwriting discounts and commissions received by the Underwriter with respect to the offering of the Shares exceeds the amount of any damages that the Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation.

(g) Non-Exclusive Remedies. The remedies provided for in this Section 10 are not exclusive and shall not limit any rights or remedies which may otherwise be available to any Indemnified Person at law or in equity.

11 Effectiveness of Agreement. This Agreement shall become effective upon the execution and delivery hereof by the parties.

12 Termination. This Agreement may be terminated in the absolute discretion of the Underwriter, by notice to the Company and the Selling Stockholders, if after the execution and delivery of this Agreement and prior to the Closing Date (i) trading generally shall have been suspended or materially limited on or by any of the New York Stock Exchange, the NYSE Amex or the Nasdaq Stock Market; (ii) trading of any securities issued or guaranteed by the Company shall have been suspended on any ex-change

or in any over-the-counter market; (iii) a general moratorium on commercial banking activities shall have been declared by federal or New York State authorities; or (iv) there shall have occurred any outbreak or escalation of hostilities or any change in financial markets or any calamity or crisis, either within or outside the United States, that, in the judgment of the Underwriter, is material and adverse and makes it impracticable or inadvisable to proceed with the offering, sale or delivery of the Shares on the Closing Date on the terms and in the manner contemplated by this Agreement, the Pricing Disclosure Package and the Prospectus.

(a) Whether or not the transactions contemplated by this Agreement are consummated or this Agreement is terminated, the Company will pay or cause to be paid all costs and expenses incident to the performance of its obligations hereunder, including without limitation, (i) the costs incident to the authorization, issuance, sale, preparation and delivery of the Shares and any taxes payable in that connection; (ii) the costs incident to the preparation, printing and filing under the Securities Act of the Registration Statement, the Preliminary Prospectus, any Issuer Free Writing Prospectus, any Pricing Disclosure Package and the Prospectus (including all exhibits, amendments and supplements thereto) and the distribution thereof; (iii) the costs of reproducing and distributing each of the Transaction Documents; (iv) the fees and expenses of the Company’s counsel and independent accountants; (v) the fees and expenses incurred in connection with the registration or qualification and determination of eligibility for investment of the Shares under the state or foreign securities or blue sky laws of such jurisdictions as the Underwriter may designate and the preparation, printing and distribution of a Blue Sky Memorandum (including the related fees and expenses of counsel for the Underwriter) not to exceed $10,000; (vi) the cost of preparing stock certificates; (vii) the costs and charges of any transfer agent and any registrar; (viii) all expenses incurred by the Company in connection with any “road show” presentation to potential investors ; and (ix) all expenses and application fees related to the listing of the Shares on NASDAQ.

(b) If (i) this Agreement is terminated pursuant to Section 12, (ii) the Selling Stockholders for any reason fails to tender the Shares for delivery to the Underwriter or (iii) the Underwriter declines to purchase the Shares for any reason permitted under this Agreement, the Company agrees to reimburse the Underwriter for all reasonable and accountable out-of-pocket costs and expenses (including the reasonable and accountable fees and expenses of their counsel) reasonably incurred by the Underwriter in connection with this Agreement and the offering contemplated hereby.

15 Persons Entitled to Benefit of Agreement. This Agreement shall inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and any controlling persons referred to in Section 10 hereof. Nothing in this Agreement is intended or shall be construed to give any other person any legal or equitable right, remedy or claim under or in respect of this Agreement or any provision contained herein. No purchaser of Shares from the Underwriter shall be deemed to be a successor merely by reason of such purchase.

16 Survival. The respective indemnities, rights of contribution, representations, warranties and agreements of the Company, the Selling Stockholders and the Underwriter contained in this Agreement or made by or on behalf of the Company, the Selling Stockholders or the Underwriter pursuant to this Agreement or any certificate delivered pursuant hereto shall survive the delivery of and payment for the Shares and shall remain in full force and effect, regardless of any termination of this Agreement or any investigation made by or on behalf of the Company, the Selling Stockholders or the Underwriter.

17 Certain Defined Terms. For purposes of this Agreement, (a) except where otherwise expressly provided, the term “affiliate” has the meaning set forth in Rule 405 under the Securities Act; (b) the term “business day” means any day other than a day on which banks are permitted or required to be closed in New York City; and (c) the term “subsidiary” has the meaning set forth in Rule 405 under the Securities Act .

(a) Notices. All notices and other communications hereunder shall be in writing and shall be deemed to have been duly given if mailed or transmitted and confirmed by any standard form of telecommunication. Notices to the Underwriter shall be given to it at J.P. Morgan Securities LLC, 383 Madison Avenue, New York, New York 10179 (fax: (212) 622-8358); Attention: Equity Syndicate Desk. Notices to the Company shall be given to it at MarketAxess Holdings Inc., 140 Broadway, 42nd Floor, New York, New York 10005, Attention: Mr. Charles R. Hood, General Counsel (fax: 212-813-6384). Notices to the Selling Stockholders shall be given at JP Morgan Chase & Co., 383 Madison Avenue, New York, New York 10179 Attention: Cristina S. Kim, Markets Strategies Strategic Investments (fax: 917-464-8841).

(b) Governing Law. This Agreement and any claim, controversy or dispute arising under or related to this Agreement shall be governed by and construed in accordance with the laws of the State of New York applicable to agreements made and to be performed in such state.

(c) Counterparts. This Agreement may be signed in counterparts (which may include counterparts delivered by any standard form of telecommunication), each of which shall be an original and all of which together shall constitute one and the same instrument.

(d) Amendments or Waivers. No amendment or waiver of any provision of this Agreement, nor any consent or approval to any departure therefrom, shall in any event be effective unless the same shall be in writing and signed by the parties hereto.

(e) Headings. The headings herein are included for convenience of reference only and are not intended to be part of, or to affect the meaning or interpretation of, this Agreement.

If the foregoing is in accordance with your understanding, please indicate your acceptance of this Agreement by signing in the space provided below.


Very truly yours,

MARKETAXESS HOLDINGS INC.

By:	/s/ Richard M. McVey
	Name:	Richard M. McVey
	Title:	Chief Executive Officer


J.P. MORGAN PARTNERS (23A), L.P.

By: J.P. MORGAN PARTNERS (23A MANAGER), LLC, its General Partner

By:	/s/ Tom Williams
	Name:	Tom Williams
	Title:	Vice President


LABMORGAN CORPORATION

By:	/s/ Luis Valdich
	Name:	Luis Valdich
	Title:	Managing Director

The undersigned understands that you, J.P. Morgan Securities LLC, (the “Underwriter”) propose to enter into an Underwriting Agreement (the “Underwriting Agreement”) with MarketAxess Holdings Inc., a Delaware corporation (the “Company”), and the Selling Stockholders listed on Schedule 1 to the Underwriting Agreement, providing for the public offering (the “Public Offering”) by the Underwriter, of Common Stock of the Company (the “Securities”). Capitalized terms used herein and not otherwise defined shall have the meanings set forth in the Underwriting Agreement.

In consideration of the Underwriter’s agreement to purchase and make the Public Offering of the Securities, and for other good and valuable consideration receipt of which is hereby acknowledged, the undersigned hereby agrees that, without the prior written consent of J.P. Morgan Securities LLC, the undersigned will not, during the period ending 60 days after the date of the prospectus relating to the Public Offering (the “Prospectus”), (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock, $0.003 per share par value, of the Company (the “Common Stock”) or any securities convertible into or exercisable or exchangeable for Common Stock (including without limitation, Common Stock or such other securities which may be deemed to be beneficially owned by the undersigned in accordance with the rules and regulations of the Securities and Exchange Commission and securities which may be issued upon exercise of a stock option or warrant), or publicly disclose the intention to make any offer, sale, pledge or disposition, (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Common Stock or such other securities, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise or (3) make any demand for or exercise any right with respect to the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock without the prior written consent of J.P. Morgan Securities LLC, in each case other than (A) the Securities to be sold by the undersigned pursuant to the Underwriting Agreement, (B) transfers of shares of Common Stock as a bona fide gift or gifts, (C) distributions of shares of Common Stock to members or stockholders of the undersigned, (D) transfers to any trust for the direct or indirect benefit of the undersigned or a member of the immediate family (as defined below) of the undersigned in a transaction not involving a disposition for value, (E) transfers to any corporation, partnership, limited liability company or other entity of all the beneficial ownership interests which are held by the undersigned or a member of the immediate family of the undersigned in a transaction not involving a disposition for value, (F) transfers by will, other testamentary document or intestate succession to the legal representative, heir, beneficiary or a member of the immediate family of the undersigned, or (G) transfers to any affiliate of the undersigned or any investment fund or other entity controlled or managed by the undersigned in a transaction not involving a disposition for value; provided that in the case of any transfer or distribution pursuant to clause

(B),(C),(D),(E), (F) or (G), each donee or distributee shall execute and deliver to the Underwriter a lock-up letter in the form of this paragraph; and provided, further, that in the case of any transfer or distribution pursuant to clause (B),(C), (D),(E), (F) or (G), no filing by any party (donor, donee, transferor or transferee) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or other public announcement shall be required or shall be made voluntarily in connection with such transfer or distribution (other than a filing on a Form 5 made after the expiration of the 60-day period referred to above). Furthermore, notwithstanding the restrictions imposed by this Letter Agreement, the undersigned may, without the prior written consent of J.P. Morgan Securities LLC, exercise any option to purchase shares of Common Stock granted under any stock incentive plan of the Company; provided that (i) any Common Stock received upon such exercise shall be subject to this Letter Agreement and (ii) no filing by the undersigned under the Exchange Act reporting a reduction of beneficial ownership shall be required or shall be made voluntarily in connection with such exercise (other than a filing on a Form 5 made after the expiration of the 60-day period referred to above).

In furtherance of the foregoing, the Company, and any duly appointed transfer agent for the registration or transfer of the securities described herein, are hereby authorized to decline to make any transfer of securities if such transfer would constitute a violation or breach of this Letter Agreement.

The undersigned hereby represents and warrants that the undersigned has full power and authority to enter into this Letter Agreement. All authority herein conferred or agreed to be conferred and any obligations of the undersigned shall be binding upon the successors, assigns, heirs or personal representatives of the undersigned.

The undersigned understands that, if the Underwriting Agreement does not become effective, or if the Underwriting Agreement (other than the provisions thereof which survive termination) shall terminate or be terminated prior to payment for and delivery of the Common Stock to be sold thereunder, the undersigned shall be released from all obligations under this Letter Agreement.

The undersigned understands that the Underwriter is entering into the Underwriting Agreement and proceeding with the Public Offering in reliance upon this Letter Agreement.

This Letter Agreement and any claim, controversy or dispute arising under or related to this Letter Agreement shall be governed by and construed in accordance with the laws of the State of New York, without regard to the conflict of laws principles thereof.


Very truly yours,

[NAME OF DIRECTOR OR OFFICER]

By:
		Name:
		Title:


Accepted: February 22, 2012

J.P. MORGAN SECURITIES LLC

By	/s/ Frank Bruni
	Name:	Frank Bruni
	Title:	Authorized Signatory

		September 30,
Selling Stockholder	Number of Shares:

J.P. Morgan Partners (23A), L.P.		800,000

LabMorgan Corporation		2,797,333