Mayo died of pneumonia and heart failure after a long illness in a nursing facility near her home in Thousand Oaks, family friend Alex Ben Block told the Los Angeles Times.
Mayo launched her movie career with a small part in the 1943 movie "Jack London," starring her future husband, Michael O'Shea. She also received billing as a Goldwyn Girl in "Up in Arms," a 1944 comedy starring Danny Kaye and Dinah Shore.
After moving to Warner Bros., Mayo gave one of her best-remembered performances, in "White Heat," director Raoul Walsh's crime saga in which Mayo played the wife of James Cagney, a mentally disturbed gang boss.
She is survived by her daughter, Mary Johnston, and three grandsons.