 His twin brother, Johnny, is a former second baseman and pitcher.O'Brien attended Saint Mary's High School in South Amboy, now Cardinal McCarrick High School, where he has been inducted into the school's sports hall of fame.He attended Seattle University, where he played on the basketball team for the Chieftains (along with his brother Johnny) and participated in a stunning 84–81 upset over the Harlem Globetrotters on January 21, 1952.