Before leaving school for Hollywood, Darnell was a student at Sunset High School, which she entered in September 1937, majoring in Spanish and art. She did not have a lot in common with her peers and usually spent her time at home as a teen, working under the guidance of her mother. In 1936, she entered the Dallas Little Theater and was cast in the southwestern premiere of "Murder in the Cathedral." The same year, she was hired as one of the hostesses at the Texas Centennial Exposition.