Tennant is best known for his work on TV's "Doctor Who" and in the Royal Shakespeare Company's recent stage production of "Hamlet."
The BBC said Tennant and Girls Aloud singer Sarah Harding will appear in "The Legend of Fritton's Gold," the sequel to 2007's "St Trinian's."
Tennant is set to play the villain Pomfrey in the movie, while Harding, who made a cameo in "St. Trinian's" with her fellow Girls Aloud band members, will play "a cool new schoolgirl," the BBC said.
The two new "St. Trinian's" movies follow up a franchise started in the 1950s, which includes the films "The Belles of St. Trinian's" and "Blue Murder at St. Trinian's."