O’Melveny Worldwide

Dimitri Portnoi is an experienced litigator who represents clients in a wide range of complex business litigation, financial service, and entertainment matters, including consumer class actions, unfair competition, business torts, fraud, contract and related commercial litigation. Dimitri has represented clients in a diverse array of industries, including entertainment, health care, natural resources, finance and banking, communications, and manufacturing. These clients have worked with Dimitri in a variety of matters, including federal constitutional cases, international law and the Alien Tort Statute, copyright and trademark law, products liability, federal anti-discrimination law, state tax litigation, consumer class actions, ERISA litigation, and contract and related commercial litigation. As a core member of the Firm’s Water industry group, Dimitri’s clients also rely on his expertise in water law and regulatory law, and call on him frequently for counsel on both litigation matters and transactions. Dimitri has worked on multiple trials, both as trial and appellate counsel, and on numerous appeals.

  • Representing medical-device manufacturers as appellate counsel in complex and ongoing products liability litigation.
  • Securing the dismissal of Fair Housing Act lawsuits brought by municipal entities against a leading global bank. 
  • Representing a financial services company in Attorney General lawsuits asserting violations of consumer protection laws, bringing a motion to dismiss in federal district court and litigating two appeals in the Ninth Circuit concerning the scope of the Class Action Fairness Act (CAFA).
  • Representing a major health services company in a class action lawsuit alleging improper reimbursement procedures and implicating significant issues of preemption under the Employment Retirement Income Security Act (ERISA).
  • Counseling a nationwide trade association concerning the federal constitutional implications of several municipalities’ proposals to exercise eminent domain authority over underwater mortgages.
  • Representing a major motion picture studio in a contract, intellectual property, and First Amendment dispute involving several successful appeals before the Ninth Circuit and extensive motion practice before the district court.
  • Defending a major energy company against a suit arising under the Alien Tort Statute, resulting in a quick and decisive victory before the district court.
  • Representing major pharmaceutical manufacturers against Medicaid reimbursement, fraud and unfair trade practices claims brought by numerous State Attorneys General in petitions to respective state supreme courts.
  • Counseling a land developer on potential challenges under California’s administrative and environmental laws to a municipality’s indefinite delay of a significant residential development project.
  • Successfully representing a group of Nevada couples seeking to overturn that State’s ban on same-sex marriage.
  • Representing before the Ninth Circuit a California prisoner in a Section 1983 challenge to his designation as a gang associate that resulted in his indefinite assignment to solitary confinement.


Bar Admissions

  • California

Court Admission

  • US District Court, Central and Eastern Districts of California, and Southern District of Texas
  • US Court of Appeals, Second, Fourth, Ninth, and Eleventh Circuits


  • New York University, J.D.: magna cum laude: Order of the Coif; Senior Articles Editor of New York University Law Review; Fellow, Center for Research in Crime and Justice; Pomeroy Scholar (top ten students in first-year class); Allen Scholar (top ten percent of students at end of second year; Paul D. Kaufman Law Review Prize (faculty-decided award for most outstanding student note)
  • Columbia University, B.A., Political Science

Honors & Awards

  • Named one of the "Best LGBT Lawyers Under 40" by the National LGBT Bar Association (2016)

Professional Activities


  • Honorable Judith W. Rogers, US Court of Appeals for the District of Columbia Circuit
  • Honorable Margaret M. Morrow, US District Court for the Central District of California


  • “Combating Organized Crime with Union Democracy: A Case Study of the Election Reform in U.S. v. International Brotherhood of Teamsters,” Loyola of Los Angeles Law Review, Vol. 42 (2009) (with Professor James B. Jacobs)
  • “Note, Resorting to Extraordinary Writs: How the All Writs Act Rises to Fill the Gaps in the Rights of Enemy Combatants,” New York University Law Review, Vol. 83 (2008)
  • “Administrative Criminal Law & Procedure in the Teamsters Union: What Has Been Achieved After (Nearly) Twenty Years,” Berkeley Journal of Employment and Labor Law, Vol. 28 (2007) (with Professor James B. Jacobs)