Tammy Tsoumas represents leading U.S. and multinational corporations in antitrust and other complex commercial litigation matters including price-fixing, monopolization, patent licensing and restraint of trade, unfair competition, wrongful death, and bankruptcy matters. She has experience in federal and state courts across the country and in complex multidistrict litigation, representing clients in diverse industries such as transportation, technology, electronics, media, manufacturing, and financial services.

In April 2018, Tammy was named to the Los Angeles Business Journal’s list of “Most Influential Women Attorneys." In 2017 and 2018, she was recognized by The Legal 500 U.S. for her antitrust work. Tammy also has been recognized as one of Southern California’s “Rising Stars” by Super Lawyers from 2013 to 2017.


Thought Leadership


Put Me In, Coach: The Ethics of Witness Preparation,” ABA Section of Antitrust Law – Compliance and Ethics Spotlight, March 2015

The Illinois Brick Wall: Standing Tall,” Journal of Antitrust & Competition, Spring 2011

Federal Circuit Issues Decision Regarding 'Patent Misuse' Affirmative Defense,” Kirkland & Ellis Alerts, April 2009


“Antitrust Monopolization Developments,” American Bar Association 2014 Spring Meeting, Los Angeles, April 2014

“The Nuts and Bolts of a Monopoly Case,” Unilateral Conduct Committee and The Young Lawyers Division Antitrust Law Committee, January 2013


“Most Influential Women Attorneys,” Los Angeles Business Journal, 2018

Recognized in The Legal 500 U.S. for Antitrust, 2017–2018

"Rising Star" Southern California Super Lawyers, 2013–2017


Admissions & Qualifications

  • 2007California


  • United States Court of Appeals for the Ninth Circuit
  • United States District Court for the Central District of California
  • United States District Court for the Southern District of California
  • United States District Court for the Eastern District of California
  • United States District Court for the Northern District of California


  • University of California, Los Angeles, School of LawJ.D.2006
    Order of the Coif
  • Brown UniversityB.A., Business Economics2003
    Attended the London School of Economics, 2001–2002