Joan Felt was born on January 18, 1932, in Elizabeth, New Jersey. Her mother was quite a famous piano player in the 1930s. Six-year-old Joan made her film debut in Walking Down Broadway (1938). She played the role of Sunny, and changed her name from Felt to Carroll. A role in Two Sisters (1938) followed, and the next year she had supporting roles in Barricade (1939) and Tower of London (1939). It wasn't until 1940 when Joan had her breakthrough. She had important parts in Anne of Windy Poplars (1940) and especially Primrose Path (1940), where she stole the show as Ginger Rogers' younger sister. In 1941 Joan won her first lead role in Obliging Young Lady (1942). She played Bridget Potter, who was stuck in the middle of a custody case but still found time to be the life of the party at a resort. The film costarred Ruth Warrick. In 1942 Joan was the first child star from Hollywood to appear in a Broadway play. This play, "Panama Hattie", gave Joan national fame, and she was featured in many magazine articles and newspapers. In 1943 she won her second lead role in Petticoat Larceny (1943), in which she played Joan Mitchell, a radio star who goes undercover to get a better feel of her roles. The film reunited Joan with Ruth Warrick. In 1944 Joan played perhaps her most famous role, that of Agnes, younger sister to Judy Garland and older sister to Margaret O'Brien in Meet Me in St. Louis (1944). In 1945 Joan had an important supporting role in The Bells of St. Mary's (1945), starring with Bing Crosby and Ingrid Bergman. That same year she appeared in Tomorrow, the World! (1944). After these films, Joan retired. Around 1940 she chose the name "Carroll" because she said it sounded musical.Up until 1940 she was the only child star to be summoned from Hollywood in order to appear in the leading role of a Broadway musical. When she wasn't acting, she was either ice-skating or playing the piano. She once captured fifth prize in a West Coast (USA) ice-skating competition in 1939 and played the piano in the footsteps of her mother, who appeared in concerts and on radio in her time.