In 1972, O'Connell was cast as a nervous barber in Eastwood's second directorial effort, High Plains Drifter, released the following year.

In 1976, O'Connell appeared as ferryman Sim Carstairs in The Outlaw Josey Wales, also directed by Eastwood.

O'Connell's other roles include portrayals in Every Which Way but Loose and its sequel Any Which Way You Can, where he played a member of a comically inept biker gang constantly being outmatched by Eastwood.

In addition to his film career, O'Connell was very active on TV throughout the 1960s and '70s, appearing in about 50 different roles on such series such as Star Trek, Rawhide, Petticoat Junction, Dennis the Menace and Quincy, M.E.

O'Connell died at his home in Sherman Oaks, California, on January 15, 2024, at the age of 94.