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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☐ Preliminary Proxy Statement

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

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material under §240.14a-12

BIOGEN 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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Your Vote Counts! BIOGEN INC. 2023 Annual Meeting Vote by June 25, 2023 11:59 PM ET BIOGEN INC. 225 BINNEY STREET CAMBRIDGE, MA 02142 V19728-P91166 You invested in BIOGEN 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 June 26, 2023. Get informed before you vote View the 2023 Notice and Proxy Statement and 2022 Annual Report with Form 10-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to June 12, 2023. 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 by Mail Submit with your prepaid envelope Vote by Phone 800-690-6903 Vote Virtually at the Meeting* June 26, 2023 Virtually at: www.virtualshareholdermeeting.com/BIIB2023 *Please check the meeting materials for any special requirements for meeting attendance.

BIOGEN INC. Annual Meeting of Stockholders June 26, 2023, 9:00 a.m. Eastern Time This proxy is solicited by the Board of Directors The undersigned hereby appoints Christopher A. Viehbacher, Michael R. McDonnell and Susan H. Alexander, and each of them (with full power to act alone), as proxies of the undersigned with all the powers the undersigned would possess if present during the 2023 Annual Meeting, and with full power of substitution in each of them to appear, represent and vote all shares of common stock of Biogen Inc. which the undersigned would be entitled to vote at the 2023 Annual Meeting of Stockholders, to be held online at www.virtualshareholdermeeting.com/BIIB2023 on Monday, June 26, 2023, at 9:00 a.m. Eastern Time, and at any adjournment or postponement thereof. The shares represented by this proxy will be voted as directed herein. If no direction is indicated, such shares will be voted FOR the election of all of the director nominees listed in Proposal 1, FOR Proposals 2, 3 and 5 and FOR 1 YEAR Option for Proposal 4. As to any other matter that may be properly brought before the meeting or any adjournment or postponement thereof, proxy holders will vote in accordance with their best judgment. Voting Items 1. Election of Directors. To elect the director nominees numbered 1a through 1j to serve for a one-year term extending until the 2024 Annual Meeting of Stockholders and until their successors are duly elected and qualified. 1a. Not Applicable 1b. Caroline Dorsa 1c. Maria C. Freire 1d. William A. Hawkins 1e. Not Applicable 1f. Jesus B. Mantas 1g. Not Applicable 1h. Eric K. Rowinsky 1i. Stephen A. Sherwin 1j. Christopher A. Viehbacher 2. To ratify the selection of PricewaterhouseCoopers LLP as Biogen Inc.’s independent registered public accounting firm for the fiscal year ending December 31, 2023. 3. Say on Pay—To approve an advisory vote on executive compensation. 4. Say When on Pay—To approve an advisory vote on the frequency of the advisory vote on executive compensation. 5. To elect Susan Langer as a director to serve a one-year term extending until the 2024 Annual Meeting of Stockholders and until her successor is duly elected and qualified. Board Recommends Voting Options Year For Against Abstain