Like so many other show biz veterans of his generation, O'Connor was on stage before he was even born. The son of circus performers turned vaudevillians, O'Connor performed with his parents as well as in a specialty act with his brothers--particularly brother Jack--during his formative years, touring the US and playing virtually every vaudeville theatre in the country. (In the 90s, O'Connor would be active in preserving the few remaining vaudeville houses and would often travel on his own dime to various small cities explaining the history of its vaudeville theatre.) At age 11, O'Connor performed for film cameras for the first time with his brothers in "Melody for Two" (1937), but it was only a featured specialty routine. In 1938, he was signed as a solo act by Paramount and slotted into "Sing, You Sinners", a Bing Crosby vehicle in which O'Connor wowed them performing "Small Fry". He played Huck in the 1938 version of "Tom Sawyer-Detective" and the title character as a youth in "Beau Geste" (1939). This first phase of his feature film career petered out and by 1940, O'Connor was back living out of a trunk on the vaudeville stage. Phase Two came in 1942 with a Universal contract. Often cast in juvenile roles, O'Connor would play a teenager even after he turned 20 in a string of low-budget, black and white musicals for the studio, usually with storylines of exuberant youths. O'Connor was often teamed with Peggy Rea or Gloria Jean, or whatever other starlet Universal was hoping to move up its ladder. During this phase, he starred in such now late-late night vehicles as "Private Buckaroo" (1942), "Get Hep to Love" (1942), "The Is the Life" (1944), "The Merry Monahans" (1944) and "Feudin' Fussin' and A-Fightin'" (1948).
In 1950, O'Connor was placed for the first time opposite a mule in "Francis", in which he played a bumbler (last in his class at West Point, eventually) who is saved from trouble in each film by a talking jackass. Universal made a fortune on these low-budget films, of which O'Connor starred in five of the six, and he was vocal then and now about hating them. Ironically, in between doing the silly "Francis" movies, Universal loaned O'Connor out to other studios where he had some of his best opportunities in big-budget musicals particularly "Singin' in the Rain", for which he won a Golden Globe Award, "Call Me Madame" (1953), opposite Ethel Merman, and "There's No Business Like Show Business" (1954), in which he was Merman's son and Marilyn Monroe's eventual husband. In 1957, O'Connor starred in the title role of "The Buster Keaton Story," but, like Keaton, whose film career waned with the coming of sound, O'Connor's waned with the decline of the studio system and the virtual end of musicals not based on Broadway shows. O'Connor was virtually off the screen in the 60s, save an appearance in an Italian film in 1961 and in "That Funny Feeling" (1965). His work on film in the 70s was limited to co-narrating and being on screen introducing the clips in "That's Entertainment!" (1974). He also had a small role in Milos Forman's "Ragtime" (1981).
In the 50s, O'Connor broke into TV--his studio, Universal, was less dogmatic about keeping its stars away from the medium. He was one of the rotating hosts of "The Colgate Comedy Hour" (NBC, 1951-54) and won an Emmy for his efforts in 1953. From 1955-56, he had a new sponsor, but the same network, for "The Donald O'Connor Texaco Show". He also performed on most of the big-name variety shows of the 50s and 60s, and, in 1968, had a short stint as the host of a talk-variety series that was syndicated as "The Donald O'Connor Show". In the 80s, O'Connor made several appearances on "The Love Boat". He also began directing in the 60s, for the stage as well as for TV commercials and TV episodics, particularly "Petticoat Junction".
There was always the stage. When film work petered out, O'Connor became a frequent headliner in Las Vegas and tried Broadway for the first time in a book musical with the short-lived and ill-advised "Bring Back Birdie" (1981), a sequel to the 60s hit "Bye Bye Birdie". In 1984, he headlined the revival of Jerome Kern's "Show Boat" as Cap'n Andy. O'Connor has also toured in numerous shows, including Neil Simon's "I Oughta Be in Pictures". In the 90s, he and Debbie Reynolds have made frequent appearances together in a stage variety show. After several notable guest appearences on television series such as "Frasier" and "The Nanny" in the mid-1990s, O'Connor made a most welcome return to the big screen alongside such other veterans as Jack Lemmon, Walter Matthau and Gloria DeHaven as a dance instructor on a cruise ship in the uneven but crowd-pleasing comedy "Out to Sea" (1997), showing in his final role that that he still had more than his share of slick moves even as a septegenerian.