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David A. O’Neil is a litigation partner and member of the firm’s White Collar & Regulatory Defense Group. Recommended by Chambers USA (2019) and The Legal 500 US (2018) as a leading lawyer in White Collar Crime & Government Investigations, his practice focuses on white collar criminal defense, internal investigations, privacy and cybersecurity, congressional investigations and AML/sanctions enforcement defense. In 2018, Mr. O’Neil was recognized as a “Litigation Trailblazer” by the National Law Journal and a “White Collar MVP” by Law 360. He is also recognized by The Legal 500 (2018) and Chambers USA (2019) where clients say he is “responsive and sharp, he spots the key issues straightaway and is able to quickly analyze and break them down in a manner to be tackled.”

Mr. O’Neil has a unique practice focused on representing clients in high-stakes matters involving significant legal, political and public relations implications. His experience spans criminal investigations by the U.S. Department of Justice and foreign law enforcement bodies, sensitive, confidential internal investigations for high-profile companies, investigations by the United States Congress, litigation brought by state Attorneys General and class action lawsuits.

Prior to joining Debevoise in January 2015, Mr. O’Neil served for eight years in prominent positions within the Department of Justice. In early 2014, the President and Attorney General designated Mr. O’Neil to lead the Criminal Division, where he was responsible for supervising more than 600 attorneys investigating and prosecuting the full range of federal crimes, including corporate malfeasance, cybercrime, fraud offenses and money laundering. Mr. O'Neil also served as Deputy Assistant Attorney General for the Fraud Section. In that capacity, he supervised more than 100 prosecutors engaged in nationwide enforcement against FCPA violations, healthcare fraud, and securities and financial fraud.

Before moving to the Criminal Division, Mr. O’Neil served for three years as Senior Associate Deputy Attorney General and Chief of Staff to the Deputy Attorney General, the Department's second-in-command. In that role, he was part of DOJ’s core management team with direct supervisory responsibility for more than two dozen attorneys. He participated in a broad range of high-profile matters, including significant FCPA prosecutions, the LIBOR investigations, and high-profile investigations of financial institutions for money laundering and Bank Secrecy Act violations.

Mr. O’Neil oversaw the DOJ’s response to multiple congressional investigations and brokered a landmark agreement with major technology companies over disclosures of government demands for customer information. In addition, Mr. O’Neil participated in negotiations with the Swiss government over the framework of Swiss cooperation in what eventually became the DOJ tax program.

In 2009, Mr. O’Neil served as Assistant to the Solicitor General. He argued three cases in the U.S. Supreme Court, authored more than 50 briefs filed with the Supreme Court, and handled appeals from high-profile white-collar criminal convictions.

Mr. O’Neil began his career at DOJ as a federal prosecutor in the U.S. Attorney’s Office for the Southern District of New York. As an Assistant U.S. Attorney, he tried numerous cases to successful jury verdicts and argued several appeals. He worked on multiple cases involving financial institutions, including bank fraud, mortgage and identity-theft matters.

Mr. O’Neil's recent publications include “Staying A Step Ahead,” International Financial Law Review (July, 2015); “Enforcement Scrutiny Falling On Individuals,” The National Law Journal (May, 2015); and “New York State Department Of Financial Services Expands Its Cyber Focus To Insurers,” FC&S Legal (April, 2015).

Mr. O’Neil earned his J.D., magna cum laude, in 2000 from Harvard Law School, where he was an editor of the Harvard Law Review. He graduated magna cum laude from Princeton University, with a B.A. in 1995.

Upon graduation from law school, he clerked for two years, first for Judge Robert D. Sack of the U.S. Court of Appeals for the Second Circuit and then for U.S. Supreme Court Justice Ruth Bader Ginsburg.


  • Harvard Law School, 2000, J.D.
  • Princeton University, 1995, B.A.

Bar Admissions

  • New York
  • District of Columbia