Watson appeared as Rose in last year's Oscar-nominated film adaption of the book and play "War Horse." She joins previously announced cast member Adam Brody and Kristen Bell in the film, to be directed by Jennifer Getzinger, a TV director and former script supervisor.
The play "Some Girl(s)" revolves around a man who revisits former lovers on the eve of his marriage to another woman. Watson will play Lindsay, a vengeful married college professor who had an affair with the man, who then skips town.
Watson is a two-time best actress Oscar nominee. She was nominated for the 1998 "Hilary and Jackie" and for the 1996 "Breaking the Waves."
LaBute, Andrew Carlberg, and Leeden Media's Chris Schwartz and Patty West are producing the film.
The Hollywood Reporter first reported the news.