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Mark Mosier represents clients in high-stakes, complex litigation in appellate and trial courts across the country, including the Supreme Court of the United States.

A former law clerk to Chief Justices William Rehnquist and John Roberts, Mr. Mosier has represented clients in more than 40 cases before the U.S. Supreme Court. He has filed briefs in many of the highest profile cases before the Court in recent terms, including the travel ban, same-sex marriage, the Affordable Care Act, partisan gerrymandering, and legislative prayer cases.

Mr. Mosier also frequently represents clients in federal and state courts of appeals. These appeals have involved a wide range of legal issues, including class actions, administrative law, government contracts, and insurance coverage disputes. He also advises clients on litigation strategy before the case reaches the appellate stage. He works closely with the trial team to ensure that issues are properly presented and preserved for appeal and, when necessary, to develop novel legal arguments that can help shape unsettled areas of law.

  • Successfully argued for Eli Lilly and Co. in the Ninth Circuit in a consumer class action case.
  • Successfully argued for Genentech in the Third Circuit in a False Claims Act case.
  • Successfully argued for government contractor in the Fourth Circuit in a multi-million dollar contract dispute with subcontractor.
  • Filed amicus briefs in the Supreme Court on behalf of the U.S. Chamber of Commerce on issues important to the business community, including class actions and deference to agency regulations.

Pro Bono

  • Presented argument in federal district court and the Fourth Circuit on behalf of individuals and organizations whose relatives and members are prohibited from entering the United States as a result of the President’s travel ban.
  • Filed amicus briefs in the Supreme Court on behalf of Senators John McCain and Sheldon Whitehouse in a partisan-gerrymandering case, on behalf of political science professors in same-sex marriage cases, and on behalf of the Center for the Administration of Criminal Law in numerous criminal matters.
  • Successfully represented an individual in the Supreme Court in a domestic violence case involving criminal contempt sanctions for violation of a protective order.

Memberships and Affiliations

  • Edward Coke Appellate Inn of Court

Previous Experience

  • University of Kansas School of Law, adjunct professor (2005)
  • San Francisco Giants, minor league baseball player (1997-1999)
  • Legal 500 US, Dispute Resolution - Appellate - Supreme Court
  • Washington DC Super Lawyers, "Rising Star"      
  • Member of University of Chicago Athletics Hall of Fame