Early roles O'Connell went into acting in 1929, landing a role in summer stock at the Frankin Stock Company in
Dorchester, Massachusetts, playing a role in
The Patsy. He made his legitimate stage debut in the middle 1930s, appearing in various roles in theater and vaudeville in the U.S, and in London. O'Connell had small film roles early in his career. His film debut was as a student in
Freshman Year (1938) and he appeared in a small role as a reporter in
Citizen Kane (1941). After
Picnic, he appeared in another
Joshua Logan film,
Bus Stop, in 1956, as the down-to-earth friend of the lead, played by
Don Murray. In that same year he appeared in
Solid Gold Cadillac, playing a kindly office manager in love with
Judy Holliday's assistant, Miss Shotgraven. His performance as
James Stewart's alcoholic mentor in
Anatomy of a Murder (1959) resulted in a second Oscar nomination. In 1962, he portrayed the father of
Elvis Presley's character in the motion picture
Follow That Dream, and in 1964 in the Presley-picture ''
Kissin' Cousins.'' In the same year, O'Connell portrayed the idealist-turned-antagonist Clint Stark in
The 7 Faces of Dr. Lao, which has become a cult classic, and in which O'Connell's is the only character other than star
Tony Randall to appear as one of the "7 faces." O'Connell continued appearing in choice character parts on both television and films during the 1960s, but avoided a regular television series, holding out until he could be assured top billing. On Christmas Day, 1962, O'Connell was cast as Clayton Dodd in the episode "Green, Green Hills" of the western series
Empire, starring
Richard Egan as the rancher Jim Redigo. This episode features
Dayton Lummis as Jason Simms and
Joanna Moore as Althea Dodd. In 1966, he guest-starred as a scientist who regretfully realized that he has created an all-powerful android (played by
James Darren) in an episode of
Voyage to the Bottom of the Sea, titled "The Mechanical Man." In the February 1967 episode "Never Look Back" of the TV series
Lassie, he played Luther Jennings, an elderly ranger who monitors the survey tower at Strawberry Peak and who takes it hard when he finds he'll lose his job when the tower is slated for destruction. In 1967, O'Connell co-starred with
Monte Markham in
The Second Hundred Years, playing the aging son of a gold miner who was frozen for a hundred years in Alaska. The series lasted for one season. He worked in commercials, playing a friendly pharmacist as a spokesperson for
Crest. He made his final film appearance in
The Hiding Place (1975), portraying a Dutch watch-maker who hides Jews during World War II.
Alzheimer's disease forced his retirement in the mid-1970s. == Personal life and death==