Platt is best remembered for her role as the officer's pregnant wife in John Ford's Stagecoach (1939). After two years on Broadway, she came to Hollywood in 1938. She returned to the New York stage in 1942 after acting in a half-dozen movies. She worked with Rex Harrison in Anne of the Thousand Days on Broadway in 1948 and in the 1950s played a variety of roles on television, including two appearances on Alfred Hitchcock Presents and a recurring role as Ruth Holden on The Guiding Light.
