05/02/2007 at 03:00 PM EDT
Jessica Simpson's acting career is turning her into a major movie star – literally.
The singer has signed on to play the title role in the comedy Major Movie Star, about a down-on-her-luck actress who enlists in the Marines, her rep tells PEOPLE.
"She's excited to get back on a movie set and get into a new character," says her rep.
Simpson, 26, who has already had starring roles in The Dukes of Hazzard and Employee of the Month, had been scheduled to being filming a spy comedy, The Witness, in June, but now she'll start shooting Major in Louisiana that month instead.
Until then, she'll be spending time with boyfriend John Mayer. "They're really happy," says a source.