The actress will co-star with Rupert Everett, Colin Firth, Lena Headey, Caterina Murino, Stephen Fry, Jodie Whittaker, Celia Imrie, Anna Chancellor, Russell Brand and Toby Jones.
St. Trinians will be directed by Oliver Parker and Barnaby Thompson and was written by Piers Ashworth and Nick Moorcroft.
The comedy follows the story of the antics of young girls who are attending a private all-girl boarding school.