Tammy Tsoumas represents leading U.S. and multinational corporations in complex commercial litigation matters including antitrust, price-fixing, monopolization, False Claims Act, restraint of trade, unfair competition, product liability, patent licensing, and wrongful death 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 2022, Tammy was named to the Los Angeles Business Journal’s list of “Leaders of Influence: Litigators & Trial Attorneys,” and in 2018 she was named to its 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 2013–2017.


Thought Leadership


Supreme Court Cautions that Companies May Not Be Able to Rely on Foreign Governments’ Interpretations of its Laws,” Kirkland & Ellis Alert, July 2018

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


“Leaders of Influence: Litigators & Trial Attorneys,” Los Angeles Business Journal, 2022

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