David O’Neil is Co-Chair of the White Collar & Regulatory Defense Group and a partner in the Washington, D.C. office.

Consistently recognized as one of the Nation’s top litigators and white collar defense attorneys, Mr. O’Neil represents companies and individuals in their highest stakes matters. His practice focuses on controversies that not only pose legal risk but also threaten political and reputational harm. He has represented the largest multinational companies and financial institutions, as well as CEOs, Board Chairs, Cabinet Secretaries, and world leaders. A former leader of the Criminal Division at the Department of Justice, Mr. O’Neil has tried numerous cases to verdict in federal court and argued six cases in the Supreme Court.

Many publications have recognized Mr. O’Neil’s litigation achievements. In 2024, he was named a finalist for The National Law Journal’s Attorney of the year and shortlisted for Global Investigations Review’s Investigations Professional of the Year. The American Lawyer has named him a “Litigator of the Year” finalist and featured him as a “Litigator of the Week” for a victory that The Washington Post hailed as “a win for democracy.” The National Law Journal recognized Mr. O’Neil twice as a Litigation Trailblazer, and Law360 named him as one of eight “White Collar MVPs” nationwide. He is ranked as a Band 1 lawyer for White Collar Crime & Government Investigations by Chambers USA (2025) where clients say that “David provides top-notch strategic advice at every turn.” He has been described as “a go-to person for a high-stakes issue” and the “rare and valued combination of brilliant lawyer, fearless strategist and exceptional leader.” Mr. O’Neil is also ranked as a leading lawyer for FCPA by Chambers USA (2025) and for Corporate Investigations and White Collar Criminal Defense by The Legal 500 US (2025).

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 of the FCPA, 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 was also an Assistant to the Solicitor General, authoring more than 50 briefs filed with the Supreme Court and handling 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 defended those verdicts on appeal.

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 from Princeton University with a B.A. magna cum laude 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.