Williamson, E. Marcellus

E. Marcellus Williamson

Retired Partner

Marc Williamson retired from the partnership in December 2023. Mr. Williamson, partner in the Washington, D.C. office, was a member of the Litigation & Trial Department, the Antitrust & Competition Practice, and the Communications Industry Group. He was also a member of the firm's Ethics Committee. Mr. Williamson focused on representing clients in complex, global antitrust matters.

Mr. Williamson represented US and international clients on all aspects of antitrust law, including merger review, price fixing investigations, and class action litigation. He 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 had 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.


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