Sebastian Alsheimer is the head of Cleary Gottlieb’s Shareholder Engagement and Activism Defense practice. He advises clients on shareholder activism defense, proxy contests, and corporate governance, and has advised on over 400 activism situations globally.

Routinely recognized as one of the leading activism defense attorneys in the U.S., Sebastian serves as legal counsel and a strategic advisor to public companies in their engagements with activist investors and other dissident shareholders. He counsels boards and management teams across the full range of activist situations, including proxy contests, withhold campaigns, consent solicitations, 13D filings, settlement negotiations, hostile takeovers, contentious M&A, and other activist tactics.

Sebastian joined the firm as a partner in January 2026 from another major international law firm. Previously, Sebastian was a partner at the leading legal advisor to activist investors, giving him distinctive insight into activist strategies and objectives.

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Selected Activities

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  • Board of Trustees, Harvard Club of New York City
  • Board of Regents, Harris Manchester College, University of Oxford

  • Board of Trustees, American-Scandinavian Foundation

Publications