Jones, best known for her work on TV's "The Office" and "Parks and Recreation," will also star in the movie, which is to be produced by Suzanne and Jennifer Todd of Team Todd.
McCormack has had recurring roles on the series "The Sopranos," "Dirt" and "In Plain Sight."
"Celeste" is about a divorcing couple who attempt to maintain their friendship while pursuing new relationships.
"Rashida is among the brightest and funniest young actresses today and we are delighted to be working with her," Overture Chief Executive Officer Chris McGurk and Chief Operating Officer Danny Rosett said in a statement. "The script she and Will have put together is witty and touching and with Team Todd in the mix, the project has great promise."
"We are such big fans of both Rashida and Will and it is exciting to be working with them creatively. Rashida is proving she's one to watch both in front of the camera and behind the scenes," Jennifer and Suzanne Todd added.
Team Todd produced the successful Austin Powers movies, as well as "Across the Universe," "Must Love Dogs," "Prime" and "Memento."
The company is currently in post-production on Tim Burton's "Alice in Wonderland," starring Johnny Depp.