Tobin was born in New York City on November 29, 1899. Her father, Thomas Tobin, a bank clerk who later became a racetrack bookmaker, was born in Nova Scotia, Canada and her mother, Genevieve, was born in Washington, DC. She had a sister Vivian and a brother George.
Tobin made her film debut in 1910 in Uncle Tom's Cabin as Eva. She appeared in a few films as a child and formed a double act with her sister Vivian. Their brother, George, also had a brief acting career. Following her education in Paris and New York, Tobin concentrated on a stage career in New York.
Although she was seen most often in comedies, she also played the role of Cordelia in a Broadway production of King Lear in 1923. Popular with audiences, she was often praised by critics for her appearance and style rather than for her talent, but in 1929, she achieved a significant success in the play Fifty Million Frenchmen. She introduced and popularized the Cole Porter song "You Do Something to Me", and the success of the role led her back to Hollywood, where she performed regularly in comedy films from the early 1930s.
She played prominent supporting roles opposite such performers as Jeanette MacDonald, Nelson Eddy, Cary Grant, Barbara Stanwyck, Claudette Colbert, Joan Blondell, and Kay Francis, but occasionally played starring roles, in films such as Golden Harvest (1933) and Easy to Love (1934). She played secretary Della Street to Warren William's Perry Mason in The Case of the Lucky Legs (1935). One of her most successful performances was as a bored housewife in the drama The Petrified Forest (1936), starring Leslie Howard, Bette Davis, and Humphrey Bogart.
