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Sean P. McDonnell

Sean P. McDonnell

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Securities Investigations: Internal, Civil and Criminal

Securities Investigations: Internal, Civil and Criminal

Guide to Anti-Corruption Laws in Major Jurisdictions


Sean P. McDonnell is a commercial litigator with experience in a wide variety of high-stakes litigation matters. An accomplished brief writer and oral advocate, Sean has handled both jury and bench trials in state and federal court, including a high-profile civil fraud case in which he represented a large financial institution seeking to recover over $40 million in fraudulently-borrowed funds.  Sean has also handled criminal matters in both state and federal court, and has represented witnesses in federal grand jury proceedings. 

Sean has substantial experience in antitrust litigation, having served as lead litigation associate in several cases involving claims advanced under Sections 1 and 2 of the Sherman Act.  He has also handled numerous significant government investigations, assisting clients with responding to SEC, Department of Justice, and Congressional demands. He regularly advises clients regarding regulatory and policy matters, including antitrust and securities law compliance. Sean has also worked on multiple intellectual property litigation matters, representing clients accused of trademark and patent infringement.

Sean has a special interest in trans-national legal issues, and he frequently assists multinational corporations with navigating the complexities and idiosyncrasies of U.S. litigation. He has written academically about the extraterritorial application and enforcement of US antitrust, securities, and general criminal laws.  He has served as lecturer at Northwestern Law School, Georgetown Law School, and Wharton School of Business at the University of Pennsylvania on these and other topics.

Sean was also a member of the litigation team that successfully represented then-candidate Rahm Emanuel against challenges to his candidacy for Mayor of the City of Chicago, culminating in a unanimous favorable decision in the Illinois Supreme Court.  He occasionally advises other political campaigns and interest groups on issues related to the First Amendment, election law, and voting rights. 

Prior to joining Mayer Brown, Sean served as law clerk to the Honorable Rebecca Pallmeyer of the United States District Court for the Northern District of Illinois. He graduated magna cum laude from Harvard Law School in 2009, where he was the Senior Policy Editor of the Harvard Law and Policy Review.

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