Barbour, 41, admitted he first fondled the aspiring actress in July 2001 in his dressing room at the Brooks Atkinson Theatre where he was performing in "Jane Eyre," the New York Daily News reported Friday.
The actor, who has portrayed the Beast in the Broadway production of Disney's "Beauty and the Beast," also confessed to forcing the then 15-year-old girl to touch him and luring her up to his apartment on the pretense of helping her with her career, then engaging in oral sex with her.
Barbour previously denied the allegations through his lawyer, claiming the now 21-year-old victim brought the charges against him after learning he had inherited money, the News said.
The actor, who lives in California, faces 60 days in prison and three years' probation when he is sentenced Feb. 29.
2014: The Year in Music [PHOTOS]