Born and raised in Alabama as Ann Steely, O'Donnell attended high school and college in Oklahoma City, Oklahoma, then worked as a stenographer to finance a trip to Hollywood, where she was spotted by a talent scout, leading to her being signed to a contract by producer
Samuel Goldwyn.
Recognizing her talent and appeal through a thick Southern accent, Goldwyn arranged rigorous voice & theatrical training at the American Academy of Dramatic Arts and elsewhere, bestowed on her a winsome Irish stage name, and cast her in
The Best Years of Our Lives (1946). This film's success boded well for Cathy's career, and soon she was starring in the now-classic
They Live by Night (1948). However, her rise in films was checked when, on Sunday, April 11th, 1948, at age 24, she married 48-year-old producer
Robert Wyler, older brother of one of Hollywood's most accomplished directors,
William Wyler, whose own long-term contract with Goldwyn had recently ended acrimoniously. The irate Goldwyn abruptly canceled her contract; thereafter she had no lasting association with any studio or producer. Her most memorable roles of the 1950s were in classic films noir, such as
Detective Story (1951), where her sincere, sweet girl-next-door persona was at odds with those films' dark, gritty milieu. Her last and most famous film was
Ben-Hur (1959), after whose enormous success she worked on TV until 1961. Belying Goldwyn's opinion, her marriage to Wyler proved happy, though childless. Her death on their 22nd wedding anniversary, Saturday, April 11th, 1970, followed a long struggle with cancer.