Then 24-year-old O'Donnell married 47-year-old Robert Wyler, the elder brother of film Director William Wyler, on April 11, 1948. She had met her husband two years earlier, while being directed by his brother in The Best Years of Our Lives (he would also direct her in Detective Story [co-written by Robert Wyler] and Ben-Hur). She died on her 22nd wedding anniversary, April 11, 1970, of a cancer-related cerebral hemorrhage following a long illness. Her husband died nine months later. The couple had no children. She is interred at Forest Lawn Memorial Park, Glendale, California.