Catherine Simonsen

Associate, Los Angeles



Catherine Simonsen is an associate in the Firm's Commercial Litigation Practice. She represents clients involved in high-stakes litigation and complex business disputes, with a particular focus on antitrust, class actions and appellate work.

Catherine has represented clients from a wide range of industries, including consumer products, technology, automotive and transportation, and entertainment, in a variety of contentious matters at the trial and appellate levels.

In her antitrust practice, Catherine has successfully prosecuted numerous competitor suits. In her active class action practice, Catherine has helped clients defeat class certification motions and secure their victories on appeal.

Catherine successfully advocates for her clients, achieving significant results that further their business interests. Her appellate experience includes successes before state and federal appeals courts. In the US Court of Appeals for the Ninth Circuit, she secured affirmance of her client's attorney's fees award. In the US Court of Appeals for the Third Circuit, Catherine secured affirmance of a class certification denial in a large, multi-state antitrust class action. In addition, she has represented clients appearing as amici curiae in the Washington Supreme Court and US Supreme Court and at the certiorari stage at the US Supreme Court.

Dedicated to pro bono work, Catherine has represented Salvadoran nationals seeking asylum, as well as a variety of non-profits before the US Supreme Court, including women's rights and gender justice organizations and a grassroots political organization.

During her time as a member and student co-director of Yale Law School's Supreme Court Advocacy Clinic, Catherine gained experience in certiorari, amicus, and merits briefing before the US Supreme Court. After law school, Catherine served as a law clerk to Judge Jerome Farris of the US Court of Appeals for the Ninth Circuit and Judge John C. Coughenour of the US District Court for the Western District of Washington.

Prior to her legal career, Catherine was an equities associate at a global investment bank in New York, where she structured and marketed over-the-counter equity derivatives to institutional and private wealth clients.

Bars and Courts
California State Bar
Washington State Bar
US District Court for the Central District of California
US District Court for the Southern District of California
US District Court for the Western District of Washington
US Court of Appeals for the Ninth Circuit
US Circuit Court for the Third Circuit
Yale Law School
Stanford University


Represented a heavy-duty truck manufacturer in antitrust litigation alleging conspiracy to monopolize the market and raise prices of Class 8 truck transmissions. Defeated plaintiff's motion for class certification. Affirmed on appeal.*

Represented movie theatre circuits in antitrust conspiracy, monopolization and tortious interference actions against competitors in DC and Atlanta District Court. Defeated competitor's motion to dismiss and secured mutually agreeable settlements.*

Represented a child airline harness manufacturer in the defense of a federal antitrust claim related to an alleged exclusive distributorship agreement. Obtained dismissal with prejudice of plaintiff's claim.*

Represented women's rights and gender justice organizations in amicus filing in support of parties challenging constitutionality of laws and practices denying same-sex couples the right to marry.*

*Matters prior to joining White & Case.


A Review of ABA Antitrust Section's Spring Meeting, Law360, April 11, 2016, (co-author)

Takeaways From The ABA Antitrust Spring Meeting: Part 3, Law360, April 5, 2017 , (co-author)

Takeaways From The ABA Antitrust Spring Meeting: Part 2, Law360, April 4, 2017, (co-author)