Sean P. Hennessy

Sean P. Hennessy

Senior Associate

Sean Hennessy focuses his practice on white collar criminal defense and complex commercial litigation. Mr. Hennessy returned to the firm after serving as a law clerk for the Honorable John D. Bates of the United States District Court for the District of Columbia.

Mr. Hennessy's white collar defense experience includes conducting internal investigations and representing companies and individuals in government investigations concerning pharmaceutical marketing, FCPA, antitrust matters, and the Lacey Act. He has also advised clients in congressional investigations.

Mr. Hennessy has represented clients in a broad range of commercial matters. His recent experience includes defending pharmaceutical companies and government contractors in civil litigation under the False Claims Act, representing private equity firms and corporate directors in business disputes, and defending pharmaceutical companies in product liability litigation. He has experience in all aspects of litigation including early case assessment, drafting dispositive motions, discovery, taking and defending depositions, expert discovery, and preparing for trial and appellate arguments.

Mr. Hennessy maintains an active pro bono practice, primarily representing criminal defendants in felony cases in DC Superior Court. In one of these cases, he obtained a jury verdict acquitting his client on all charges in an aggravated assault trial.

Mr. Hennessy graduated from Georgetown University Law Center, where he was Executive Editor of the Georgetown Journal of International Law, participated in the Appellate Litigation Clinic, and was a member of the moot court team. Upon graduation, Mr. Hennessy was elected to the Order of the Coif. Prior to law school, Mr. Hennessy was a management consultant.


  • Major pharmaceutical company in a series of cases (including those combined within an MDL) brought by government prosecutors, third-party payors, and private individuals alleging fraudulent marketing of opioids for long-term pain and seeking damages, restitution, and civil penalties.
  • Private equity firm and corporate directors in litigation involving breach of fiduciary duty.
  • Importer in a criminal investigation under the Lacey Act.
  • Former corporate executive in FCPA investigation by DOJ and SEC.
  • Sales executive of pharmaceutical manufacturer as counsel in criminal antitrust investigation by DOJ.
  • Pharmaceutical manufacturer as counsel in internal investigation focused on sales representative promotional activities.
  • Bristol-Myers Squibb and Sanofi as counsel in Plavix product liability litigation and multiple False Claims Act cases.
  • Government contractor in False Claims Act litigation.


Washington, DC Super Lawyers
"Rising Star"– Business Litigation, Criminal Defense: White Collar (2021)


  • JD, Georgetown University Law Center, 2012, magna cum laude, Order of the Coif
  • MA, Economics, Fordham University, 2001
  • BA, Economics, Loyola University Maryland, 2000, magna cum laude
  • District of Columbia
  • Maryland
  • US District Court, District of Maryland
  • US District Court, District of Columbia, The Honorable John D. Bates

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