Born in Staten Island, New York, Sexton made his film debut at age 14 in Todd Solondz's Welcome to the Dollhouse playing the troubled bully Brandon McCarthy, for which he was nominated for an Independent Spirit Award. He was the lead in Hurricane Streets, which won 3 awards at Sundance, and also appeared in the Oscar-winning film Boy's Don't Cry, Black Hawk Down, and Session 9 as well as cult films Empire Records and Pecker. He recently had a pivotal role in Martin McDonagh's Oscar-winning film Three Billboards Outside Ebbing, Missouri. On television, he played Belko on AMC's Emmy and Golden Globe nominated series The Killing, recently had a supporting role in El Camino: A Breaking Bad Movie, and plays the enigmatic character "Horse" on the acclaimed Netflix series Russian Doll with Natasha Lyonne.