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.           )

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☐ Preliminary Proxy Statement

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☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Pursuant to §240.14a-12

AFFILIATED MANAGERS GROUP, 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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AMG AFFILIATED MANAGERS GROUP, INC. 777 SOUTH FLAGLER DRIVE WEST PALM BEACH, FL 33401 Your Vote Counts! AFFILIATED MANAGERS GROUP, INC. 2022 Annual Meeting Vote by May 26, 2022 11:59 PM ET D76491-P71827 You invested in AFFILIATED MANAGERS GROUP, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the stockholder meeting to be held on May 27, 2022. Get informed before you vote View the Notice and Proxy Statement and Form 10-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 13, 2022. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. For complete information and to vote, visit www.ProxyVote.com Control # Smartphone users Point your camera here and vote without entering a control number Vote in Person at the Meeting* May 27, 2022 2:00 PM BST (9:00 AM EDT) Affiliated Managers Group Ltd. 35 Park Lane London W1K 1RB United Kingdom *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. V1.1

Vote at www.ProxyVote.com THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. Please follow the instructions on the reverse side to vote these important matters. Voting Items Board Recommends 1. To elect eight directors of the Company to serve until the 2023 Annual Meeting of Stockholders and until their respective successors are duly elected and qualified. Nominees: 1a. Karen L. Alvingham For 1b. Tracy A. Atkinson For 1c. Dwight D. Churchill For 1d. Jay C. Horgen For 1e. Reuben Jeffery III For 1f. Félix V. Matos Rodríguez For 1g. Tracy P. Palandjian For 1h. David C. Ryan 2. To approve, by a non-binding advisory vote, the compensation of the Company’s named executive officers. For 3. To ratify the selection of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the current fiscal year. For NOTE: Such other business as may properly come before the meeting or any adjournment or postponement thereof. Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. D76492-P71827