Sean McDonnell is a partner in Mayer Brown's Washington DC office and a member of the global Litigation & Dispute Resolution practice. Previously, Sean was an Assistant United States Attorney (AUSA) in the US Attorney’s Office for the Eastern District of Pennsylvania.

During his tenure as a federal prosecutor, Sean first-chaired several jury trials to verdict and oversaw large-scale investigations, including complex wiretap and forensic financial investigations. He prosecuted a variety of cases involving, among other things, tax fraud, wire fraud, insurance fraud, bank fraud and public corruption. Most recently, he served as the US Attorney’s coordinator for COVID-19-related government fraud cases, including all cases that involved the CARES Act and Paycheck Protection Program (PPP) and Economic Injury Disaster Loans (EIDL) fraud investigations.

Before his AUSA stint, Sean was a litigator in Mayer Brown’s Chicago and Washington DC offices, where he represented corporate clients in white collar investigations and various civil litigation matters, including antitrust and securities cases. Earlier in his career, he clerked for the Honorable Rebecca Pallmeyer of the US District Court for Chicago and served as an appellate law clerk for the Cook County State’s Attorney’s Office. He regularly teaches classes on managing legal risk at the University of Pennsylvania’s Wharton Business School, including a recent “Crash Course on Internal Investigations” seminar for Wharton’s executive education program.

Spoken Languages

  • English
Securities Investigations: Internal, Civil and Criminal


Harvard Law School, JD, magna cum laude
Senior Policy Editor, Harvard Law and Policy Review

University of Missouri, BA, magna cum laude
Phi Beta Kappa


  • District of Columbia
  • Illinois


  • US Court of Appeals for the Third Circuit
  • US Court of Appeals for the Seventh Circuit
  • US District Court for the District of Columbia
  • US District Court for the Eastern District of Pennsylvania
  • US District Court for the Northern District of Illinois
  • US District Court for the Eastern District of Wisconsin