O'Brien died Tuesday at the Motion Picture and Television Hospital in Woodland Hills. She was 81.
A striking dark-haired beauty who, one critic wrote, had all the "expression of a wall clock," O'Brien was featured in the best of the MGM musicals, including "Ziegfeld Follies," "Till the Clouds Roll By," "The Harvey Girls," "Thousands Cheer" and "Du Barry Was a Lady."
O'Brien was born in Los Angeles, where her father was a captain in the Police Department and her uncle was the city's postmaster. She became interested in dancing after seeing Eleanor Powell in several movies, but quickly turned to singing.
She was cast in the Los Angeles stage production of "Meet the People" in 1940, by a director who liked her imitation of Ethel Merman.
But on opening night, O'Brien had a terrible case of the jitters. She went onstage and remembered every word to the song she performed, but sang with a blank, wide-eyed stare and a seemingly frozen face.
The audience, thinking her performance a gag, howled with laughter. And although O'Brien was less than pleased with her performance, she was consoled by the fact that Louis B. Mayer, the head of Metro-Goldwyn-Mayer, had seen the show and liked it.
After a screen test, O'Brien was signed to a seven-year contract and was, in the 1940s, one of the studio's top comic actresses. She appeared with reigning stars including Judy Garland, Mickey Rooney, Fred Astaire, Burt Lahr and the Marx Brothers. She made seven films with Red Skelton and one with Donald O'Connor.
By the end of the 1940s, however, the studio system was starting to fade and many contract players, including O'Brien, were faced with difficult circumstances.
She shifted to nightclubs and small theater productions for most the rest of her career. She also was a guest on popular TV comedy and variety shows hosted by Ed Sullivan, Merv Griffin and Steve Allen. In the 1990s, she appeared in the Palm Springs Follies.
She is survived by her son, John Feggo; three daughters, Terri O'Brien, Liz Watkins and Gale Evans; seven grandchildren; and two great-grandchildren.
Memorial services are pending.