O’Melveny Worldwide

Henry Thumann devotes his practice to high-stakes antitrust matters. He has spent a significant amount of time defending mergers and acquisitions before the U.S. antitrust agencies—the Federal Trade Commission (FTC) and the Department of Justice (DOJ)—for clients in an array of industries, including defense, healthcare, computer, supermarket, food products, gaming, and manufacturing.


Bar Admissions

  • California
  • District of Columbia


  • Harvard Law School, LL.B., 1960: magna cum laude; Law Review, (1958-1960) 
  • University of Illinois, B.S., 1957

Honors & Awards

  • Recognized by Best Lawyers® for Commercial Litigation in Washington, DC (2022-2024); Henry has been listed in Best Lawyers® since 1989.
  • Recommended in litigation by the Euromoney Legal Media Group Expert Guides
  • Recommended in antitrust by Chambers USA 

Professional Activities


  • Ninth Circuit Judicial Council Committee on Evaluation of Judges and Lawyers (1985-2005)
  • Center For Public Resources Antitrust Committee (1986-present)
  • Ninth Circuit Judicial Conference (1982-85), (executive committee (1984 85))
  • Executive Committee, Antitrust Section, Los Angeles County Bar Association (1989-present) 


  • Ninth Circuit Judicial Conference, lawyer representatives (1984-1985)
  • ABA Standing Committee on Aeronautical Law (1974-1977) 
  • Los Angeles County Bar Association, 1986


  • American College of Trial Lawyers