2026 Annual Meeting of

Stockholders and Proxy Statement

Tuesday, June 9, 2026

9:00 a.m. Eastern Time

To be held online at:

www.virtualshareholdermeeting.com/BIIB2026

April 28, 2026

Dear Fellow Stockholders

On behalf of the Board of Directors, I thank you for your investment in Biogen and for the confidence you have placed in the Board’s stewardship of your interests. Biogen is focused on delivering long-term value for our stockholders with a high-conviction late-stage pipeline with the potential to drive both meaningful innovation and sustained growth. We made notable progress on this strategy in 2025, where execution on commercialization of our growth products and a sharpened development pipeline focused on neurology, immunology, and rare disease are laying a strong foundation for Biogen’s future.

Key milestones of our progress in 2025 include:

In early 2026, we entered into a merger agreement with Apellis Pharmaceuticals, Inc. which, upon completion, is expected to bolster Biogen’s near and long-term growth prospects with the addition of EMPAVELI² and SYFOVRE³ and accelerate entry into nephrology and retinal diseases.

In 2025, we continued to strengthen the Board with the addition of a director who brings deep experience and a distinguished record of leadership in research and development across the life sciences and biopharmaceutical sectors. Our newest director further enhances the Board’s oversight of our strategic direction as we expand our portfolio.

Biogen remains committed to broadening access to high quality healthcare for patients worldwide. In 2025, we advanced our standard for patient-first clinical research, highlighted by completing enrollment for the TOPAZ Phase 3 lupus clinical trials. Lupus disproportionately affects young women, especially women of color, and the trials were intentionally designed to include this cohort. By selecting sites in highly affected communities and addressing real-world barriers like transportation and childcare, we created a trial experience that met patients where they are. Further, in 2025, Biogen and the Biogen Foundation contributed approximately $35 million in grants, donations, sponsorships and in-kind contributions to broaden access to healthcare, address the fundamentals of community health and strengthen the life sciences talent pipeline.

My service as a director and Chair of the Board will conclude at the 2026 Annual Meeting. I extend my sincere thanks to our stockholders for their confidence over the past sixteen years, and to my fellow directors, past and present, with whom it has been a privilege to serve. Our Board’s breadth of experience across life sciences and global innovation strengthens oversight. We are better able to deliver long-term value for our stockholders because our Board recognizes the benefit of experience as well as new ideas. I have strong conviction that the Board, under the leadership of Dr. Maria C. Freire as incoming Chair, together with the management team, led by Chris Viehbacher, is well positioned to guide Biogen through its next chapter of growth.

Thank you for your continued support of our efforts.

Caroline Dorsa

Chair of the Board

Executive Pay Structure Aligns with Compensation Philosophy

Our Track Record of Responsiveness to Stockholder Feedback

Our Board values the views of our stockholders and solicits input from them throughout the year. Following the 2025 Annual Meeting where our Say on Pay proposal received 67.7% support, the CMDC and our Board conducted stockholder engagement to better understand stockholder perspectives. We engaged stockholders to get feedback on a range of topics including specific aspects of our business strategy, capital allocation, corporate governance, and our executive compensation practices. All of the stockholder engagement calls were led by our Board and CGC Chair and attended by the Chairs of the CMDC and/or Audit Committee and/or other independent directors.

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Executive Pay Structure Aligns with Compensation Philosophy

The feedback and perspectives received from stockholders during these meetings were shared with the Board and served as an input to discussions at the Board and its committees, and ultimately informed decisions we made and actions we took for long-term value creation for our stockholders. We have also enhanced disclosures regarding the topics discussed during these stockholder engagement meetings. The table below provides a summary of the executive compensation-based feedback we received from stockholders, how the Board incorporated the feedback into its actions, and how these actions enhance stockholder value.

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Executive Pay Structure Aligns with Compensation Philosophy

Executive Pay Structure Aligns with Compensation Philosophy

How Our Pay Practices Align with Our Philosophy

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Board Composition Highlights

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Notice of 2026 Annual Meeting of Stockholders

By Order of Our Board of Directors,

Wendell Taylor,

Chief Corporation Counsel, Secretary

225 Binney Street

Cambridge, Massachusetts 02142

April 28, 2026

This Notice of 2026 Annual Meeting of Stockholders and Proxy Statement are first being sent to stockholders on or about April 28, 2026.

Our 2025 Annual Report on Form 10-K is being sent with this Notice of 2026 Annual Meeting of Stockholders and Proxy Statement.

Table of Contents

Table of Contents

2026 Proxy Statement

DEFINED TERMS

2026 Proxy Statement

Proxy Statement Summary

Proxy Statement Summary

This summary highlights important information you will find in this Proxy Statement. As it is only a summary, please review the complete Proxy Statement before you vote.

Vote Right Away Through Advance Voting Methods						Vote During Meeting
		Vote by Internet Using Your Computer Go to www.proxyvote.com and enter the Control Number provided in your Notice of Internet Availability of Proxy Materials (Notice), or if you received a printed copy of proxy materials, on your proxy card or voting instruction form.						Vote During the Meeting See Part 1 –“General Information About the Meeting” for details on how to vote during the Annual Meeting.
		Vote by Telephone Call 800-690-6903 or the telephone number on your Notice, proxy card or voting instruction form. You will need the Control Number provided on your Notice, or if you received a printed copy of the proxy materials, on your proxy card or voting instruction form.
		Vote by Mail Complete, sign and date the proxy card or voting instruction form and mail it in the accompanying pre-addressed envelope.

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Proposal 1 — Election of Directors

Proposal 1 — Election of Directors

We are asking our stockholders to elect the 10 director nominees listed below to each serve a one-year term extending until our 2027 annual meeting of stockholders and until he or she is duly elected and qualified, unless they resign or are removed:

Our Board has nominated these 10 individuals based on its carefully considered judgment that the skills, contributions, backgrounds, perspectives and experiences of our nominees qualify them to serve on our Board. As described in detail below, our nominees have considerable professional and business expertise. We know of no reason why any nominee would be unable to accept nomination or election. All nominees have consented to being named in this Proxy Statement and to serve if elected.

To be elected, a director nominee must receive the affirmative vote of a majority of the votes cast. Abstentions and broker non-votes, if any, are not considered votes cast under our bylaws and will have no effect on the results of this vote. For additional information please see also “What vote is required to approve each proposal and how are votes counted?” on page 68. If any nominee is unable to serve on our Board, the stock represented by your proxy will be voted for the election of such other person as may be nominated by our Board or alternatively, the number of directors may be reduced accordingly by our Board. In addition, in compliance with all applicable state and federal laws and regulations, we will file an amended proxy statement and proxy card that, as applicable, (1) identifies the alternate nominee(s) and (2) discloses that such nominee(s) has consented to being named in the revised proxy statement and to serve if elected.

* Age and Committee memberships are as of April 21, 2026.

** Ms. Dorsa has notified the Board that she is not standing for reelection at the 2026 Annual Meeting. Effective immediately after the 2026 Annual Meeting, Dr. Freire will become Chair of the Board. The Board will appoint a new CGC Chair following the 2026 Annual Meeting.

C – Chair; M – Member

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Proposal 1 — Election of Directors

Summary of Director Nominee Core Experiences and Skills

Our Board is comprised of highly qualified leaders in their respective fields, and as a group possesses a deep and broad set of skills, contributions, backgrounds, perspectives and experiences that facilitate strong oversight and strategic direction for a pioneering biotechnology company. Our Board and our CGC believe the skills, contributions, backgrounds and experiences of our directors provide us not only with a wide range, but also the appropriate mix, of perspectives to effectively address our evolving needs and represent the best interests of our stockholders.

The following chart summarizes the competencies and background of each director nominee. The details of each nominee’s competencies are included in each nominee’s biography.

Key Skills and Experience

Executive Leadership & Business Operations Experience serving in a senior leadership role develops skills in core management areas and provides a valuable practical understanding of the operations of complex organizations

✓

✓

✓

✓

✓

✓

✓

✓

✓

✓

Commercial Knowledge of creating and sustaining revenue streams facilitates oversight of efficient and robust revenue generation

✓

✓

✓

✓

✓

✓

Cybersecurity/Information Technology/AI Experience understanding and overseeing information technology and cybersecurity matters is critical to mitigating risks to our business and to Board oversight of Biogen’s actions to address innovation and competitiveness in a rapidly evolving technological age

✓

✓

✓

Drug Development Expertise of drug development increases successful navigation of the highly regulated life sciences market

✓

✓

✓

✓

✓

✓

✓

Healthcare & Pharma Leadership Experience as an executive and/or in an operational role at a pharmaceutical or biotechnology focused organization or company provides directors with a deep understanding of Biogen’s business and key strategic and operational considerations

✓

✓

✓

✓

✓

✓

✓

✓

✓

✓

Finance and Accounting Expertise in finance, capital markets, mergers and acquisitions, investment management and financial reporting processes enables directors to effectively monitor and assess Biogen’s operating and strategic performance and capital allocation decisions, and oversee accurate financial reporting and robust controls

✓

✓

✓

✓

✓

✓

✓

International Business Global market expertise enhances oversight of strategy development and execution, supply chain and compliance across markets

✓

✓

✓

✓

✓

✓

Public Board Service Corporate governance fluency ensures stockholder interests serve as input to discussions and informs Board decisions

✓

✓

✓

✓

✓

✓

✓

✓

Government and Public Policy Understanding of the complex regulatory and governmental environment in which Biogen operates allows the Board to oversee the company’s long-term strategy by incorporating current and potential changes in public policy and regulation

✓

✓

✓

✓

✓

✓

✓

✓

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Proposal 1 — Election of Directors

Key Skills and Experience

Medicine and Scientific Research Knowledge of relevant sciences and research experience provides Directors with a deep understanding of Biogen’s key therapeutic areas and an appreciation for our mission to deliver breakthroughs that change patients’ lives

✓

✓

✓

✓

✓

✓

Background

Gender

F

M

F

M

M

M

M

M

M

M

Racially/Ethnically Diverse

✓

✓

✓

Did not Disclose Demographic Background

✓

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Proposal 1 — Election of Directors

OUR BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” EACH OF THE NAMED NOMINEES. PROXIES WILL BE

VOTED “FOR” THE ELECTION OF THE NOMINEES UNLESS OTHERWISE SPECIFIED.

Set forth below is biographical information for each nominee and a summary of the specific skills, contributions, background and experiences which led our Board to conclude that each nominee should serve on the Board at this time.

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Proposal 1 — Election of Directors

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Proposal 1 — Election of Directors

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Proposal 1 — Election of Directors

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Proposal 1 — Election of Directors

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Proposal 1 — Election of Directors

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Corporate Governance

Corporate Governance

Corporate Governance Highlights

We believe that our Board’s primary functions are to appoint and evaluate our CEO and hold management accountable, oversee strategy and strategic direction, oversee key strategic, operational and compliance risks and work to achieve optimal capital allocation that maximizes long-term stockholder value. We are committed to the highest standards of ethics, business integrity and corporate governance, which we believe will help ensure that our company is managed for the long-term benefit of our stockholders. Our governance practices are designed to establish and preserve accountability for our Board and management, provide a structure that allows our Board to set objectives and monitor performance, facilitate the efficient use of resources and enhance stockholder value.

Our Corporate Governance Principles are reviewed at least annually by the CGC and are amended from time to time in response to changing regulatory requirements, evolving governance practices and trends and issues raised by our stockholders. In addition, Board members are also subject to our Code of Business Conduct. Our Corporate Governance Principles, together with our committee charters, Bylaws, Certificate of Incorporation and Code of Business Conduct, comprise our governance framework, each of which may be found at our website, www.biogen.com, under the “Corporate Governance” subsection of the “Investors” section of the website.

How our corporate governance practices align with our key governance principles is set forth in the table below.

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Corporate Governance

Commitment to Stockholder Engagement

We value the views of our stockholders and feedback received from them serves as a valuable input to Board and committee discussions and informs actions designed to increase long-term stockholder value. To support maintaining an open dialogue with our stockholders, the CGC leads our Board’s efforts on director-stockholder engagement and directs discussions with stockholders to the appropriate Board and committee members. To demonstrate our commitment to stockholder engagement, we have adopted a practice in recent years that our independent directors, led by our Chair, seek to engage with our largest stockholders to better understand their perspectives on a variety of issues, including our business strategy, capital allocation, corporate governance, executive compensation and corporate social responsibility initiatives.

In addition, our CFO and investor relations group lead our management team in investor meetings throughout the year to discuss our business, strategy and financial results. Meetings included in-person and virtual meetings, telephone and webcast conferences.

We remain committed to regular dialogue with our stockholders to increase transparency and better understand our stockholder base and their perspectives. 

Board Leadership Structure

Independent Chair Leadership

The Board regularly reviews its leadership structure to evaluate whether this structure continues to best serve the needs of the company and its stockholders. We believe that having an independent Chair promotes a greater role for independent directors in the oversight of the company, including overseeing the strategic direction of the company and oversight of material risks facing the company. Additionally, it encourages active participation by the independent directors in the work of our Board, enhances our Board’s role of representing stockholders’ interests and improves our Board’s ability to supervise and evaluate our CEO and other NEOs. Further, separation of the Chair and CEO roles allows our CEO to focus on operating and managing the company while leveraging our independent Chair’s experience and perspectives. Ms. Dorsa, an independent director, currently serves as the Chair of our Board. Ms. Dorsa has notified the Board that she is not standing for reelection at the 2026 Annual Meeting. Dr. Freire, also an independent director, will assume the role as Chair immediately after the 2026 Annual Meeting. Among other responsibilities, our Chair:

Director Independence

All of our directors and nominees for director, other than Mr. Viehbacher, our President and CEO, satisfy the Nasdaq independence requirements, as determined by our Board. All members of the Board’s standing committees satisfy the Nasdaq independence requirements. In addition, all members of our Audit Committee and our CMDC meet the additional SEC and Nasdaq independence and expertise requirements applicable specifically to audit and compensation committee members, respectively, as determined by our Board.

Process for Selecting Directors and Director Qualifications

Board Composition

Board composition is one of the most critical areas of focus for our Board. Reflecting our Board’s commitment to refreshment, seven of our independent directors have joined since 2019. Our CGC screens and recommends candidates for nomination by the full Board and, among other things, considers feedback received during the annual Board and committee evaluation process and stockholder engagement, our qualification guidelines and skills matrix and director commitment levels. Candidates who are recommended by stockholders will be considered in the same manner as other candidates. For all potential candidates, our CGC will consider all factors it deems relevant, including at a minimum those listed below in the subsection entitled “Director Qualifications.” Director nominations are recommended by our CGC to our Board and must be approved by our Board. For more information on the process for nomination of directors by stockholders please see “Stockholder Proposals” on page 72.

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Corporate Governance

Director Qualifications

Our Nomination Processes

Our CGC leads our Board’s process for identifying, evaluating and selecting directors. Our CGC uses a variety of methods to help identify potential Board candidates and considers an assessment of current Board skills, backgrounds, perspectives and experiences to evaluate candidates for recommendation to our Board for approval. Our CGC assesses potential candidates based on their history of achievement, the breadth of their business experiences, whether they bring specific skills or expertise in areas that our CGC has identified as desired and whether they possess personal attributes and experiences that will contribute to the sound functioning of our Board.

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Corporate Governance

Our Board’s process (i) leverages the Board’s succession and refreshment practices to identify skills and expertise needed on our Board, (ii) uses an independent search firm to support our CGC in conducting a broad search through a diverse pool of potential candidates and to help identify, evaluate and conduct diligence on potential candidates and (iii) provides stockholders with greater transparency on the nomination process and its objectives. Our process comprises the following:

Board Succession Planning and Refreshment

Our CGC continually reviews our Board’s composition to identify the skills needed on our Board to help oversee our company both in the near term and into the future. Ongoing strategic board succession planning, along with our average board tenure policy, are designed to ensure that our Board continues to maintain an appropriate mix of skills, backgrounds, perspectives and experiences to provide fresh perspectives and effective oversight and guidance to management.

Our CGC evaluates what additional skills and expertise may be needed near term and in the future based on the company’s strategy and potential director departures. Our CGC then compares those skills to those of the current directors to identify additional skills and experiences that would be beneficial to our Board. Our CGC then seeks to identify and recruit individuals who have the qualifications identified through this process.

Our Board does not believe that arbitrary term limits on directors’ service are appropriate. In 2023, in consideration of a number of factors, including stockholder feedback, we amended our Corporate Governance Principles to eliminate our age-based resignation policy and instituted a policy that seeks to maintain an average tenure of 10 years or less for independent directors. We believe this policy promotes better succession planning by balancing the benefit of fresh perspectives that new directors may bring with the institutional knowledge and experience that longer-tenured directors possess.

Board Committee Refreshment

Our Board, led by our CGC, reviews and determines the composition of committees and appoints the committee Chairs. Through periodic committee refreshment, we balance the benefits derived from continuity and depth of experience with those gained from fresh perspectives and enhancements to our directors’ understanding of different aspects of our business.

Regular Board and Committee Evaluations

Board and committee evaluations are critical to supporting the effective functioning of our Board. Through evaluations, our directors review where they believe our Board functions effectively and, importantly, areas where our Board believes there may be opportunities for improvement.

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Corporate Governance

CEO and Management Succession Planning

Our Board strives to ensure that we have the right management talent to pursue our strategies successfully. Our entire Board is involved in the critical aspects of CEO and other senior management succession planning processes, including establishing selection criteria that reflect our business strategies, identifying essential capabilities and competencies, and evaluating potential candidate(s). Succession is regularly discussed with the CEO as well as without the CEO present in executive sessions of our Board. Our Board and our CMDC meet at least once a year to conduct a detailed talent review that includes an assessment of the company’s talent strategies, leadership pipeline and succession plans for key executive positions. The Board also maintains a confidential emergency succession plan for the CEO, reviewed at least annually, to guide the orderly transfer of the CEO’s responsibilities in the event of an unexpected resignation, termination, death, or extended incapacity. We believe that maintaining our strong culture and adhering to our principles will ensure that we attract, retain and develop the right talent to lead the company and successfully execute our corporate strategy in the future.

Annual Elections and Majority Voting

Directors are elected by a majority of the votes cast in uncontested elections and by a plurality of votes cast in contested elections. In addition, when a director is nominated for election to the Board, directors must submit an irrevocable resignation that will be effective upon (1) the failure to receive the required number of votes for reelection at the next annual meeting of stockholders at which the directors stand for reelection and (2) acceptance of such resignation by our Board. If an incumbent director fails to receive the number of votes required for reelection, our Board (excluding the director in question) will, within 90 days after certification of the election results, decide whether to accept the director’s resignation, taking into account such factors as it deems relevant. Such factors may include the stated reasons why stockholders voted against such director’s reelection, the qualifications of the director and whether accepting the resignation would cause the company to fail to meet any applicable listing standards or would violate state or federal law. Our Board will promptly disclose its decision in a filing with the SEC.

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Corporate Governance

Committees and Meetings

Our Board met six times in 2025. Our Board also has three standing committees, the Audit Committee, CMDC and CGC. The principal functions of each committee, the committee composition as of December 31, 2025, and the number of committee meetings held in 2025 are described in the table below. The Chair of each committee periodically reports to our Board on committee deliberations and decisions. Our Board maintains charters of each of its committees and the charters are reviewed at least annually. The charters for each of the committees are posted on our website, www.biogen.com, under the “Corporate Governance” subsection of the “Investors” section of the website. Our Corporate Governance Principles, together with our committee charters, Bylaws, Certificate of Incorporation and Code of Business Conduct, comprise our governance framework.

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Corporate Governance

The Board’s Role in Risk Oversight

Our Board believes that a fundamental part of risk management is identifying and understanding the risks we face, monitoring these risks and adopting appropriate controls and strategies designed to mitigate such risks. We have a company-wide ERM program to identify, mitigate and monitor enterprise level risks that may affect our ability to achieve the company’s objectives. Our Board oversees an enterprise-wide approach to risk management, which is designed to support execution of our strategy and achievement of our objectives to improve long-term operational and financial performance, preserve our reputation and enhance stockholder value. Our Board and its committees review our risk framework and governance and oversee management’s exercise of its responsibility to assess, monitor and manage the company’s significant risk exposures.

In determining the allocation of risk oversight responsibilities, our Board and its committees generally oversee material risks within their identified areas of responsibility. Our Board and each of its committees meet regularly with management to confirm that management is exercising its responsibility to identify relevant risks and is adequately assessing, monitoring and taking appropriate action to mitigate these risks. In the event a committee receives a report from members of management on areas of material risk to the company, the Chair of the relevant committee, assisted by management where appropriate, reports on the discussion to the full Board at the next Board meeting. This enables our Board and its committees to coordinate their oversight of risk and identify risk interdependencies.

The ERM program is overseen by our Executive Committee, acting as the ERM Committee. On an ongoing basis, the ERM Committee evaluates the greatest risks to our business, their underlying risk drivers and the associated mitigation activities and controls. Annually, the ERM Committee provides our Board with a detailed review of the ERM program and key enterprise-level and emerging risks. Emerging risks that do not rise to the level of enterprise-level risk are assessed and actively managed and monitored by senior management.

A summary of the primary areas of risk oversight responsibility of our Board and each of its committees is set forth below:

Compensation Risk Assessment

The Compensation Discussion and Analysis section of this Proxy Statement describes the compensation policies, programs and practices that apply to our executive officers (which we define as all employees at the level of Vice President and above), including our NEOs listed on page 35. Our goal setting, performance assessment and compensation decision-making processes described in the CD&A generally apply to all employees. Our executive compensation comprises three components: salary, an STI program and an LTI program. Our STI program for 2025 had the same company performance goals, payout levels (as a percentage of target) and administrative provisions for all participants globally, regardless of the participant’s job level, location or function in the company. Additionally, our LTI program provides different forms of awards based upon an employee’s level but is otherwise consistent throughout the company.

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