Donnelly was an FBI agent who worked with Carter on numerous occasions. He helped dismantle HR in season 2, and was fierce in his pursuit of The Man in the Suit (John Reese). He eventually became obsessed with the case, using steadily more extreme methods of investigation. He eventually discovered that Carter was aiding Reese and was attempting to turn them in to the FBI when he was killed by Reese's old CIA partner, Kara Stanton.