Platt, who also stars in "Pitch Perfect 2," will portray a local bartender who worships Ricki (to be played by Streep). Jonathan Demme directs the film that has a screenplay by Diablo Cody.
Platt will also return to nightlife venue 54 Below Aug. 18 for an evening of pop, R&B and musical theatre songs.
The script features Streep as a woman who, seeking fame and fortune as a rock star, abandoned her family. Decades later, she decides to be a mother again to her estranged children, one of whom is going through a divorce. Marc Platt produces the film that also stars Rick Springsteen.