Caissie Levy is mainly known for her work in musical theatre on Broadway and in the West End. Her early Broadway credits included Penny Pingleton in Hairspray and Sheila in Hair, a role she also played in the West End. She originated the role of Molly Jensen in the West End and Broadway productions of Ghost: the Musical, and played Fantine in the 2014 Broadway revival of Les Misérables. Levy also originated the role of Elsa in Frozen on Broadway. For her performance on the cast recording of Caroline, or Change, she was nominated for the Grammy Award for Best Musical Theater Album in 2023. Levy originated the role of Diana Goodman in the London production of Next to Normal and received a nomination for the Laurence Olivier Award for Best Actress in a Musical.