Davis will be the soaring soloist in the Act Two opener of the Broadway smash, and will play ensemble roles, a spokesman confirmed.
Davis, a hefty actress-singer with short-cropped hair and a rich belt, was seen as a favorite to win the Fox TV talent contest until producers kicked her out in February because she had appeared on an adult website.
Jonathan Larson penned book, music and lyrics for Rent, the La Bohème-inspired rock musical that tells the story of East Village friends and lovers in the age of AIDS. Larson won the Tony Award and Pulitzer Prize, posthumously. He died of an aortic aneurysm on the eve of the show's Off-Broadway run.
Performances continue at the Nederlander Theatre.
