Born in the Bronx, NY, to an upper-middle-class Irish family, Carroll O'Connor's father was a well-connected attorney and his mother was a school teacher. The family lived well, in the Forest Hills section of Queens, until O'Connor's father ran afoul of the law and was convicted of fraud. Despite this setback in the family's well-being, O'Connor managed to attend college and considered a career as a sportswriter, but those aspirations were interrupted by the outbreak of World War II. Rejected by the United States Navy, he enrolled instead in the Merchant Marine Academy, but he later abandoned that pursuit, instead becoming a merchant seaman. After the war, O'Connor considered journalism as a career, but a trip to Dublin in 1950 changed the course of his life, as he discovered the acting profession. While attending college in Dublin, he began appearing in productions of the Gate Theater and also at the Edinburgh Festival, where he played Shakespearean roles. Returning to New York in 1954, he and his wife worked as substitute schoolteachers while he looked for acting work, which he found, after a long dry spell in which he despaired of ever getting a break, in Burgess Meredith's production of James Joyce's Ulysses. O'Connor got a role in which he received favorable notice from the critics, and that, in turn, led to his breakthrough part, as a bullying, greedy studio boss in an off-Broadway production of The Big Knife.
O'Connor jumped next to television, at the very tail-end of the era of live TV drama in New York. Beginning in 1960 with his portrayal of the prosecutor in the Armstrong Circle Theater production of The Sacco-Vanzetti Story, he established himself on the small screen as a good, reliable character actor, who was able to melt into any role with which he was presented. Over the next decade, O'Connor worked in everything from Westerns to science fiction. He played taciturn landowners, likable aliens, enemy agents (on The Man From U.N.C.L.E., in "The Green Opal Affair"), and other character roles with equal aplomb. He also appeared in several unsold television pilots during the 1960s, including The Insider with David Janssen, and Luxury Liner starring Rory Calhoun, playing character roles; and he did a pilot of his own, Walk in the Night -- directed and co-written by Robert Altman -- in which he co-starred with Andrew Duggan. O'Connor's movie career followed quickly from his television debut, starting with appearances in three dramatic films (most notably Lonely Are the Brave) in 1961. He was one of many actors who managed to get "lost" in the sprawling 20th Century Fox production of Cleopatra, but he fared better two years later in Otto Preminger's epic-length World War II drama In Harm's Way. O'Connor, playing Commander Burke, was very visible in his handful of scenes with John Wayne and Kirk Douglas, and Preminger thought enough of the actor to mention him by name along with the other stars in the film's trailer. He had major supporting roles, serious and comedic, respectively, in such high-profile movies as Hawaii and What Did You Do in the War, Daddy?, of which the latter proved critical to his subsequent career.