His parents were Eileen Ryan and Leo Penn. He studied at Santa Monica High School and entered the LA Group Repertory Théâtre where he worked as a technician and became assistant to Pat Hingle. He directed with success a play, Terrible Jim Fitch, and performed on stage in Earthworms et The girl on the Via Fleminia. After he studied drama with Peggy Feury, he sttled in New York. He had great reviews when he played Heartland, directed by Art Wolff and had a role in Taps, directed by Harold Becker. He continued to work both for theater and cinema, with directors like Louis Malle, Richard Benjamin, John Schlesinger, Dennis Hopper, Brian de Palma. The Indian Runner was his first film.