 With encouragement from Miles Mander, Maguire and her family moved to Hollywood in September 1936.Mander gave her an introduction to fellow Australian expat John Farrow, who arranged for an interview with a casting director that led to a contract with Warner Bros.

Maguire made her U.S. debut in the B movie "That Man's Here Again" with comedian Hugh Herbert, followed by "Confession" with Kay Francis and Ian Hunter, "Alcatraz Island" with Ann Sheridan and John Litel, and "Sergeant Murphy" with Ronald Reagan.In February 1938, she left Warners for 20th Century Fox.