Rebecca Mermelstein


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Rebecca Mermelstein is a first-chair trial lawyer with extensive experience handling white collar and finance-related investigations and litigation. She advises corporate and individual clients on complex white collar matters, including regulatory actions, internal investigations, and compliance initiatives.

Prior to joining O’Melveny, Rebecca spent more than a decade as an Assistant U.S. Attorney in the U.S. Attorney’s Office for the Southern District of New York. She was a senior member of the Securities and Commodities Task Force before rising to Co-Chief of the General Crimes Unit. Rebecca has tried 12 cases to verdict, briefed and argued numerous federal appeals, and conducted or supervised more than 1,000 investigations, including grand jury investigations and cross-border matters involving simultaneous investigations by multiple U.S. and international regulators. Her expertise spans securities and accounting fraud, insider trading, Ponzi schemes, money laundering, cybercrime, public corruption, human trafficking, and sexual misconduct.

Through her work leading investigations and prosecutions, Rebecca has established strong working relationships with U.S. Attorney’s Office colleagues and officials at the Securities and Exchange Commission, Commodity Futures Trading Commission, and the Public Company Accounting Oversight Board, as well as federal law enforcement agencies. The knowledge she has gained from her experience and relationships helps her achieve the best possible results for clients.


Bar Admissions

  • New York
  • New Jersey

Court Admissions

  • United States District Court, Southern District of New York
  • Second Circuit Court of Appeals


  • Harvard Law School J.D., 2005: cum laude
  • Columbia College, B.A., Comparative Religion, 2001: magna cum laude; Phi Beta Kappa 

Professional Activities


  • Honorable Charles P. Sifton, Eastern District of New York
  • Supervised dozens of jury trials and more than 1,000 cases involving securities fraud, wire fraud, mail fraud, tax fraud, money laundering, access device fraud, cybercrime, immigration offenses, child exploitation, human trafficking, robbery, narcotics trafficking, and firearms offenses.
  • Investigated and prosecuted complex financial crimes, including accounting fraud, insider trading, market manipulation, investment adviser fraud, wire fraud, bank fraud, insurance fraud, and money laundering. Managed relationships with FBI and SEC, among other agencies.
  • Conducted 12 criminal trials, including numerous multi-defendant white-collar cases. Briefed and/or argued more than a dozen appeals in the Second Circuit.
  • Investigated, prosecuted, and supervised numerous sex-crimes cases, including leading the investigation and prosecution of a 19-defendant international sex-trafficking ring and supervising multiple cases of sex abuse by middle school and high school teachers.