Shanley Caswell was born and raised in Sarasota, Florida. Shanley began acting in local theater at the age of eight. While in high school, she became involved with "Teen Source", a theater troupe whose focus is to educate the teenage community on social issues. She moved to Los Angeles to further her career in 2007, where she landed many guest-starring roles. Her first work was modelling aged 15. She also studied cultural anthropology at UCLA.
She made her feature film debut in Mending Fences, a movie for the Disney Channel and made her first major film role as one of the leads in the Horror film Detention, with her starring as Riley Jones. She appeared in horror film The Conjuring, in the supporting role Andrea Perron, her second feature film, and recently starred as the lead role in the fairy tale update Snow White: A Deadly Summer.