Thomas S. O’Neill is a Co-Chair of the firm’s Energy Practice and a member of the Litigation Department. He has served as a lawyer in private practice and in various leadership roles at Exelon, one of America’s leading energy providers, uniquely positioning him to help clients navigate the changing energy landscape from both a legal and business perspective. Mr. O’Neill brings a breadth of experience, particularly through his C-suite roles, in strategic planning, board counsel, risk management, crisis management, and project execution and provides clients with an added level of executive judgment. He guides clients through disruptions in the industry that lead to regulatory changes, jurisdictional disputes, litigation, and corporate restructurings.

Mr. O’Neill began his legal career at Jenner & Block in 1989 and was promoted to partner in 1997. He gained experience in all aspects of federal and state civil and criminal litigation, including with trials, class actions, and internal investigations for a range of corporate and individual clients, with an emphasis in complex commercial civil litigation. 

In 2001, Mr. O’Neill left Jenner & Block to join Exelon Corporation as an associate general counsel in the company’s Nuclear Generation business. He later took over Exelon Nuclear’s licensing function, which was his first assignment outside of a legal role. In that position, he was responsible for the day-to-day Nuclear Regulatory Commission interface as to all plant operations and technical specifications, and he oversaw emergency preparedness and environmental compliance.

In 2007, Mr. O’Neill moved into a generation development role, leading several projects in which he gained transferable knowledge about the industry and about business more generally. He led various high-profile projects, including, among others, forming an entity to market Exelon Nuclear’s world class operating capabilities in domestic and international markets. 

In 2010, Mr. O’Neill transferred to the regulated utility side of the business when he became General Counsel and Senior Vice President of Energy Policy at Exelon’s Commonwealth Edison subsidiary.   

Mr. O’Neill was named Exelon’s Corporate General Counsel in 2017. In that role, he served as the chief legal officer overseeing all legal and corporate governance services to the corporation and all operating units. 

Among Mr. O’Neill’s many achievements include negotiation of two major Illinois energy bills; an unprecedented settlement with US government in nuclear fuel litigation; development of the then-largest US urban solar plant; development and start-up of generation and transmission new business ventures; and winning the largest defamation jury verdict in Northern Illinois.

Throughout his career, Mr. O’Neill has been a dedicated pro bono advocate. His prior work at Jenner & Block included several murder trials and a habeas case where he won outright reversal of a state juvenile murder conviction obtained through a coerced confession. He continued his pro bono advocacy at Exelon, where the law department is nationally recognized as a pro bono leader. He also has established himself as a committed leader in diversity equity and inclusion, in part through his service to the Leadership Council for Legal Diversity (LCLD), including as a member of its board of directors from 2019 to 2020.