Peggy O'Rourke was born in Florida, but her life took a dramatic turn when her parents divorced at a young age. Her mother remarried a wealthy attorney named Stewart, and Peggy took his name. She grew up in Atlanta, where she developed impressive athletic skills that would later serve her well in her many westerns for Republic Pictures.
During a family vacation to Los Angeles to visit her grandmother, Peggy attended classes at a dramatic school on a whim. To her surprise, she caught the acting bug and decided to stay with her grandmother instead of returning to Atlanta. As fate would have it, a resident of their apartment building was character actor Henry O'Neill, who took a liking to Peggy and helped her land her first film role in Wells Fargo (1937).
Peggy's early success led to more small roles, and she eventually worked her way up to bigger parts and more frequent work. In 1940, she married actor Don 'Red' Barry, and the couple signed with Republic Pictures, Barry's studio, to make westerns and serials. Over the next three years, Peggy appeared in almost 30 films, mostly westerns, and starred in two of the studio's most successful serials.
However, Peggy soon grew tired of working on serials, preferring the feature westerns that didn't take as long to film. Her frustration with Republic eventually led her to ask for her release, which she was granted. Although she wanted to explore other genres, her extensive work at Republic made it difficult for her to find work in any other field. She freelanced for various small studios, including Monogram, Allied Artists, and PRC, until she was picked up by Columbia Pictures, which promptly cast her in serials.
Peggy eventually decided to leave the film business in 1953, but not before making some television appearances and performing in the Los Angeles theatrical community. She continued to make occasional appearances in low-budget westerns, made-for-TV movies, and horror pictures, keeping her hand in the film business while raising her family.