William Regner is a member of Debevoise’s Mergers & Acquisitions, Technology, Media & Telecommunications, Financial Institutions and Corporate Governance Groups. He is a member of the firm’s Management Committee and previously served as Deputy Chair of the firm’s Corporate Department. He focuses on public company transactions and corporate governance matters and advises boards, special committees and senior management on governance issues, including activist challenges and risk management. He has experience across many industries but is particularly active in the TMT and asset management sectors. He also regularly represents investment banking firms in their roles as financial advisors in major transactions. Mr. Regner was recognized as a “Client Service All-Star” by BTI Consulting in 2018.

Mr. Regner is ranked as a leading M&A lawyer by Chambers Global (2023) and Chambers USA (2023), where he receives praise for his “great perspective and judgment,” and where clients note his “practical approach,” “command of details and balanced view.” Sources have also said he “has the knowledge and experience, but his approach is pragmatic, commercial and practical” and that he has “outstanding technical knowledge and commercial awareness” and “comes up with creative solutions.” Clients have also said that Mr. Regner “really commands a room but is also a very good listener” and has “superb negotiating and drafting” skills. He is also recommended by The Legal 500 US, where one client has declared that he is “the best attorney of all I have used in 50 years of business.” Other sources have described him as “thoughtful, smart and savvy” and lauded his delivery of “high-value and to-the-point advice.” He is also recognized by IFLR1000 (2022) as a leading M&A lawyer.

Mr. Regner is a frequent speaker on legal developments affecting mergers and acquisitions. Recent engagements include: “Special Committees in M&A Transactions” (2022) at the Practising Law Institute’s Mergers & Acquisitions 2022: Advanced Trends and Developments conference; “Contract Enforcement Issues” (2021) at the Practising Law Institute’s Mergers & Acquisition 2021: Advance Trends and Developments conference; “Advising a Special Committee in Mergers & Acquisitions” (2020) at the Practising Law Institute’s Mergers & Acquisitions 2020: Advanced Trends and Developments conference; “Advising the Board of Directors in an M&A Transaction: An Overview of the Board’s Responsibilities” (2018 & 2019) at the Practising Law Institute’s Mergers & Acquisitions 2018 & 2019: Advanced Trends and Developments conferences; “Bank M&A Mechanics and Regulatory Issues” at FIRMA’s Current Risk Issues seminar (2017); and “The Deal: A View of Delaware Law Developments from M&A Practitioners” at the Practising Law Institute’s Delaware Law Developments 2017: What All Business Lawyers Need to Know seminar (2017). Mr. Regner also moderated a discussion on “Disclosure Matters and Other SEC Considerations in M&A” for the Practising Law Institute’s Mergers & Acquisitions 2017: Advanced Trends and Developments conference (2017).

Mr. Regner is the co-author of Takeovers: A Strategic Guide to Mergers & Acquisitions (Wolters Kluwer Law & Business, 2020) and is a contributor to Corporate Governance: Law and Practice (Matthew Bender 2013). His published articles include “How Shareholder Activists Are Targeting Insurers,” Law360 (November, 2023); “Delaware holds target cannot recover lost-premium damages,” Westlaw Today (November, 2023); “Debevoise & Plimpton Discusses Fifth Circuit Decision to Uphold Nasdaq Board Diversity Rule,” CLS Blue Sky Blog (October, 2023); “2023 Proxy Season in Review,” Harvard Forum on Corporate Governance (August, 2023); “Del. Ruling May Signal New Era Of Board Accountability,” Law360 (August, 2023); “Board Responsibility for AI Risk Oversight,” Directors and Boards (August, 2023); “Debevoise Discusses Super Voting Preferred Stock,” CLS Blue Sky Blog (April, 2023); “Debevoise & Plimpton Discusses the Mindbody Problem,” CLS Blue Sky Blog (March, 2023); “Special Committees and M&A: A Half-Year Report,” The M&A Lawyer (September, 2022); “US And UK Share Purchase Agreements: Comparing Approaches,” Practical Law (January, 2015) and “How Sell-Side Advisors Can Reduce Litigation Risk in Light of Delaware’s Rural/Metro Decision,” Journal of Investment Compliance, Volume 15 Issue 2 (August, 2014). He is also a contributing author of The Private Equity Primer: The Best of the Debevoise & Plimpton Private Equity Report and the Debevoise & Plimpton Private Equity Report. Mr. Regner co-chairs the annual ALI-CLE course on corporate mergers and acquisitions.

Mr. Regner joined Debevoise as an associate in 1994 and became a partner in 2002. Mr. Regner received his A.B. from Colgate University in 1988 and his J.D. summa cum laude from the Benjamin N. Cardozo School of Law in 1994, where he was articles editor of the Cardozo Law Review.


  • Yeshiva University, Benjamin N. Cardozo School of Law, 1994, J.D.
  • Colgate University, 1988, A.B.

Bar Admissions

  • New York