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

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☐	Soliciting Material Pursuant to §240.14a-12

Marsh & McLennan Companies, 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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*** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting to Be Held on May 20, 2021. MARSH & McLENNAN COMPANIES, INC. Meeting Information Meeting Type: Annual Meeting For holders as of: March 22, 2021 Date: May 20, 2021 Time: 10:00 A.M. EDT Location: Meeting live via the Internet-please visit www.virtualshareholdermeeting.com/MMC2021 The company will be hosting the meeting live via the Internet this year. To attend the meeting via the Internet please visit www.virtualshareholdermeeting.com/MMC2021 and be sure to have the information that is printed in the box marked by the arrow XXXX XXXX XXXX XXXX (located on the following page). MARSH & McLENNAN COMPANIES, INC. 1166 AVENUE OF THE AMERICAS You are receiving this communication because you hold shares in NEW YORK, NY 10036 the company named above. 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. P50592 proxy See the materials reverse and side voting of this instructions. notice to obtain D45984—

Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: NOTICE AND PROXY STATEMENT ANNUAL REPORT How to View Online: Have the information that is printed in the box marked by the arrow XXXX XXXX XXXX XXXX (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: 1) BY INTERNET: www.proxyvote.com 2) BY TELEPHONE: 1-800-579-1639 3) 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 XXXX XXXX XXXX XXXX (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 6, 2021 to facilitate timely delivery. How To Vote Please Choose One of the Following Voting Methods Vote By Internet: Before The Meeting: Go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow P50592 XXXX XXXX XXXX XXXX (located on the following page) available and follow the instructions. - During The Meeting: Go to www.virtualshareholdermeeting.com/MMC2021. Have the information that is printed in the box marked D45985 by the arrow XXXX XXXX XXXX XXXX (located on the following page) 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.

Voting Items The Board of Directors recommends you vote FOR the following directors: The Board of Directors recommends you vote FOR the Item 1 Election of Directors following proposals: Item 2 Advisory (Nonbinding) Vote to Approve Named 1a. Anthony K. Anderson Executive Of?cer Compensation 1b. Oscar Fanjul Item 3 Ratification of Selection of Independent Registered Public Accounting Firm 1c. Daniel S. Glaser 1d. H. Edward Hanway 1e. Deborah C. Hopkins 1f. Tamara Ingram 1g. Jane H. Lute 1h. Steven A. Mills 1i. Bruce P. Nolop 1j. Marc D. Oken 1k. Morton O. Schapiro 1l. Lloyd M. Yates 1m. R. David Yost—P50592 D45986

D45987-P50592