Marcus made her Broadway debut as Brooke Lohst in Be More Chill at the Lyceum Theatre in February 2019, after originating the role first at Two River Theatre in 2015, and then again off-Broadway at the Signature Theatre in the summer of 2018
She appeared as Amy in Company at Barrington Stage Company alongside Aaron Tveit. She received praise for her performance.
In winter 2018, she played Brigid in The Humans at the St. Louis Repertory Theatre, and was subsequently nominated for a BroadwayWorld Regional Theatre Award as Best Supporting Actress in a Drama. She also received a JJ Award from the St. Louis Post Dispatch for her performance alongside Kathleen Wise.
Marcus is also a singer and songwriter, and performs regularly with her band around New York City. She released her debut EP, Never Really Done with You, in July 2016 at Joe's Pub.
Marcus appears in the 2021 American biographical musical drama film Tick, Tick... Boom!.