O'Connor was born into an Irish immigrant family of vaudeville entertainers. As a toddler, he and his sister were involved in a road accident, which resulted in her death. His father died of a heart attack only a few weeks later. Yet it was as a comedy actor and a song-and-dance man that he became famous. His boyish looks did not allow him to take a romantic lead, except when appearing with a bigger star such as Ethel Merman (in Call Me Madam) or Bing Crosby (with whom he appeared in his first film at the age of eleven). However, he did have a separate Hollywood career in the late 1930s, in which he played such incongruous roles as Beau Geste. During World War II, he was re-invented as a star of musical films.
When the heyday of the film musical was over, O'Connor returned to the stage, and had a short-lived television series during the late 1960s. After overcoming a drinking problem in the 1970s, he continued to make film and television appearances into the 1990s. O'Connor was still making public appearances well into 2003.
Among his last words, he is reported to have expressed thanks for the Academy Award for Lifetime Achievement which he expected to win at some future date. He left his wife, Gloria, and four children.
