[1] Stewart was born in West Palm Beach, Florida, where she was raised, the daughter of John Francis O'Rourke and Frances Velma (McCampbell) Splane, who were from Bessemer, Alabama.

[2][3] She distinguished herself as a swimming champion in high school;[2] in the 1930s, her family moved to California, where she met character actor Henry O'Neill who recommended her to Paramount Pictures executives who were looking for a new actress for the part of Joel McCrea's teenage daughter in Wells Fargo (1937).

[2] In April 1944, Stewart signed a contract with Republic Pictures and began starring in Western B movies opposite such actors as Allan Lane, Sunset Carson, and Wild Bill Elliott.

In 1958, she was cast as Etta Jackson, the romantic interest of the painter Hurley Abbott, played by Brad Johnson, in the episode "The Underdog" of the ABC/Desilu western series, The Life and Legend of Wyatt Earp, with Hugh O'Brian in the title role.

She played a minor part in a 1993 episode of Seinfeld titled "The Implant", in which she portrayed the aunt of George Costanza's girlfriend.

[2] From 1993 till her death, Stewart appeared as a special guest at the annual Lone Pine Film Festival.