In 1937 O'Neil debuted in film in the movie "Stella Dallas" and in 1939 she was cast in the role of Ellen O'Hara, Scarlett O'Hara's mother, in "Gone with the Wind".
In 1937 O'Neil debuted in film in the movie "Stella Dallas". In 1939, at the age of 28, she was cast in the role of Ellen O'Hara, Scarlett O'Hara's mother, in "Gone with the Wind".