UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No.        )

Filed by the Registrant þ

Filed by a Party other than the Registrant ¨

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¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

þ Definitive Additional Materials

¨ Soliciting Material Pursuant to § 240.14a-12

MarketAxess Holdings Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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¨ Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

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(2) Aggregate number of securities to which transaction applies:

(3) Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 0-11 (set forth the amount on which the filing fee is calculated and state how it was determined):

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¨ Fee paid previously with preliminary materials.

¨ Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

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*** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Shareholder Meeting to Be Held on June 07, 2012 MARKETAXESS HOLDINGS INC. Meeting Information Meeting Type: Annual Meeting For holders as of: April 10, 2012 Date: June 07, 2012 Time: 10:00 AM EDT Location: InterContinental New York Barclay Hotel 111 East 48th Street New York, NY 10017 MARKETAXESS HOLDINGS INC. 299 PARK AVENUE NEW YORK, NY 10171 Investor Address Line 1 Investor Address Line 2 Investor Address Line 3 Investor Address Line 4 Investor Address Line 5 John Sample 1234 ANYWHERE STREET ANY CITY, ON A1A 1A1 You are receiving this communication because you hold shares in the above named company. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. B A R C O D E See the reverse side of this notice to obtain proxy materials and voting instructions. Broadridge Internal Use Only Job # Envelope # Sequence # # of # Sequence # 0000142502_1 R1.0.0.11699

Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: 1. Combined Document 2. Notice & Proxy Statement How to View Online: Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com. How to Request and Receive a PAPER or E-MAIL Copy: If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request: BY INTERNET: www.proxyvote.com BY TELEPHONE: 1-800-579-1639 BY E-MAIL*: sendmaterial@proxyvote.com If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow (located on the following page) in the subject line. Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 24, 2012 to facilitate timely delivery. How To Vote Please Choose One of the Following Voting Methods Vote In Person: Many shareholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow available and follow the instructions. Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card. Internal Use Only 0000142502_2 R1.0.0.11699

Voting items The Board of Directors recommends that you vote FOR the following: 1. Election of Directors Nominees 01 Richard M. McVey 02 Steven L. Begleiter 03 Dr. Sharon Brown-Hruska 04 Roger Burkhardt 05 Stephen P. Casper 06 David G. Gomach 07 Carlos M. Hernandez 08 Ronald M. Hersch 09 John Steinhardt 10 James J. Sullivan The Board of Directors recommends you vote FOR proposals 2, 3, 4. and 5. To ratify the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the year ending December 31, 2012. To approve, on an advisory basis, the compensation of the Company’s named executive officers as disclosed in the 2012 Proxy Statement. To approve the adoption of an amendment and restatement of the MarketAxess Holdings Inc. 2004 Stock Incentive Plan (as amended and restated effective April 28, 2006)(which, if approved, will be renamed the MarketAxess Holdings Inc. 2012 Incentive Plan) and the performance criteria used in setting performance goals for awards intended to be performance-based under Code Section 162(m). To approve the adoption of an amendment and restatement of the MarketAxess Holdings Inc. 2009 Code Section 162(m) Executive Performance Incentive Plan and the performance criteria used in setting performance goals thereunder. NOTE: UNLESS OTHERWISE SPECIFIED BY THE UNDERSIGNED, THIS PROXY WILL BE VOTED FOR THE ELECTION OF THE NOMINEES FOR DIRECTOR LISTED ABOVE AND FOR PROPOSALS 2,3,4 AND 5, AND WILL BE VOTED BY THE PROXYHOLDERS AT THEIR DISCRETION AS TO ANY OTHER MATTERS PROPERLY TRANSACTED AT THE MEETING OR AT ANY POSTPONEMENT OR ADJOURNMENT THEREOF. TO VOTE IN ACCORDANCE WITH THE BOARD OF DIRECTORS’ RECOMMENDATIONS, JUST SIGN BELOW - NO BOXES NEED BE CHECKED. Broadridge Internal Use Only xxxxxxxxxx xxxxxxxxxx Cusip Job # Envelope # Sequence # # of # Sequence # 0000142502_3 R1.0.0.11699

Reserved for Broadridge Internal Control Information NAME THE COMPANY NAME INC. - COMMON 123,456,789,012.12345 THE COMPANY NAME INC. - CLASS A 123,456,789,012.12345 THE COMPANY NAME INC. - CLASS B 123,456,789,012.12345 THE COMPANY NAME INC. - CLASS C 123,456,789,012.12345 THE COMPANY NAME INC. - CLASS D 123,456,789,012.12345 THE COMPANY NAME INC. - CLASS E 123,456,789,012.12345 THE COMPANY NAME INC. - CLASS F 123,456,789,012.12345 THE COMPANY NAME INC. - 401 K 123,456,789,012.12345 THIS SPACE RESERVED FOR SIGNATURES IF APPLICABLE Broadridge Internal Use Only Job # Envelope # Sequence # # of # Sequence # 0000142502_4 R1.0.0.11699