Witherspoon's Pacific Standard production banner and Kidman's Blossom Films will produce the film.
The two actresses are already in the postproduction stage on a limited series based on Moriarty's "Big Little Lies" for HBO, reported Deadline.
The series was adapted by David E Kelley and directed by Jean-Marc Vallee and stars Witherspoon, Kidman, Shailene Woodley, Laura Dern, Zoe Kravitz and Alexander Skaarsgard.
"Truly Madly Guilty", explores fundamental relationships like marriage, sex, parenthood and friendship through a fateful event.
The story takes place over a weekend, among six adults and three cute kids.