Cathy O'Donnell (July 6, 1923 – April 11, 1970) was an American actress, best known for her many roles in film-noir movies. While under contract with Samuel Goldwyn, O'Donnell made her debut in an uncredited role as a nightclub extra in Wonder Man (1945).

Her first major role in The Best Years of Our Lives (1946), playing Wilma Cameron, the high-school sweetheart of double amputatee Homer Parrish, played by real-life World War II veteran/amputee Harold Russell. She was loaned out to RKO for one of her most memorable films, They Live by Night (1949) starring with Farley Granger, widely considered a classic of the noir genre and on the Guardian's list of the top ten noir films. The film was directed by Nicholas Ray.