Marc Williamson, partner in the Washington, D.C. office, is a member of the Litigation & Trial Department, the Antitrust & Competition Practice, and the Communications Industry Group. He is also a member of the firm's Ethics Committee. Mr. Williamson focuses on representing clients in complex, global antitrust matters.

Mr. Williamson represents US and international clients on all aspects of antitrust law, including merger review, price fixing investigations, and class action litigation. He has obtained clearance of numerous mergers, acquisitions, and joint ventures from the Federal Trade Commission, the Department of Justice, the European Commission, and numerous other competition agencies around the world. He has extensive experience in leading multi-jurisdictional merger clearance processes.

Mr. Williamson has worked with a range of industries, including:

  • Telecommunications and media
  • Healthcare and life sciences
  • Professional services
  • Energy
  • Aerospace
  • Automotive
  • Consumer goods and services

Mr. Williamson is recognized as one of the 500 Leading Litigators in America by Lawdragon.

Mr. Williamson acted as lead global antitrust counsel in numerous industry-changing transactions, including:

  • Entercom Communications in connection with DOJ’s second request investigation and approval of its acquisition of CBS Radio
  • Integra LifeSciences Holdings Corporation in its US$1.045 billion acquisition of Johnson & Johnson’s Codman Neurosurgery business, winning approval following phase two investigations in the United States, UK, and Spain 
  • Carlyle’s acquisition of Symantec’s Veritas software business, securing six unconditional clearances globally
  • The sale of Veyance Technologies to Continental AG, obtaining 13 clearances globally, through a process that included six second phase investigations and coordinated remedy negotiations with several jurisdictions
  • The proposed merger of Omnicom Group with Publicis, securing 13 unconditional clearances globally
  • Multiplan’s acquisition of Viant, obtaining unconditional clearance after a Department of Justice Second Request investigation
  • DG Fastchannel’s acquisition of Vyvx, securing unconditional clearance after a Department of Justice Second Request investigation
  • Arch Wireless’ acquisition of Metrocall, obtaining unconditional clearance after a Department of Justice Second Request investigation

Representative litigations include:

  • Defending The Carlyle Group in Dahl, et al. v. Bain Capital, et al. (Sherman Act class action)
  • Defending United Components, Inc, in In re Aftermarket Filters Antitrust Litigation (Sherman Act class action)
  • Defending Britax in v. Toys “R” Us, et al. (Sherman Act class action)
  • Defending Oracle, in US v. Oracle (Clayton Act merger challenge)

Mr. Williamson is admitted to practice before the US Supreme Court, various US Courts of Appeals (Second Circuit, 11th Circuit and Federal Circuit), various US District Courts (Southern District of NY, Eastern District of NY, Western District of NY and District of D.C.), and the US Court of International Trade.

Thought Leadership

Mr. Williamson regularly writes and speaks on topics related to antitrust and competition. His publications and presentations include:

  • Co-author, “Private Equity Buyers As Divestiture Buyers: U.S. and EU Perspectives,” March 2019 
  • Presenter, “Merger control in the Americas,” Global Competition Review Live Merger Control Conference, October 2018
  • Co-author, “DOJ Files Unusual Suit to Unwind a Consummated Merger: 3 Lessons,” Latham & Watkins Client Alert No. 2216, September 29, 2017
  • Co-author, “Annual HSR Threshold Adjustments Announced,” Latham & Watkins Client Alert No. 1916, January 21, 2016
  • Co-author, “FTC Limits Investment Rental Property Exemption,” Latham & Watkins Client Alert No. 1860, July 29, 2015
  • Presenter, “The Role of Intent in the Assessment of Unilateral Conduct,” International Competition Network, December 2013
  • Co-author, “FTC Takes Hard Line on Premerger Filing Requirements,” Latham & Watkins Client Alert No. 1539, June 26, 2013
  • Co-author, “$500,000 Fine for CEO Highlights Risk of Vesting Shares,” Latham & Watkins Client Alert No. 1267, December 20, 2011
  • Co-author, “Consortium Deals May Move Forward: US Federal District Court Dismisses Antitrust Challenge to Private Equity Funds’ Consortium Deal,” Latham & Watkins SmartCapital Newsletter No. 6, May 2008
  • Co-presenter, “Antitrust Issues in Private Equity Investing,” ABA Section of Antitrust Law, 2008 Spring Meeting, March 26, 2008
  • Co-author, “Hot Docs vs. Cold Economics,” 47 Ariz. L. Rev. 609, 2005
  • Co-presenter, “Cartel Enforcement and Litigation in the EU and the US,” Latham & Watkins Presentation, February 18, 2003
  • Co-author, “Litigating the Fix: FTC v. Libbey, Inc. – A Private Party Perspective,” ABA Clayton Act Newsletter, December 2002

Bar Qualification

  • District of Columbia


  • JD, New York University School of Law, 1988
  • MA, Columbia University, 1986
  • BA, Swarthmore College, 1984

Languages Spoken

  • English
  • French