Written by M.A. Larson, Pennyroyal's Princess Boot Camp is a modern-day fairytale about a school that shapes girls into warrior princesses to battle against an ever-growing terror of wicked witches.
The film adaptation will be developed under Witherspoon's Pacific Standard production company, with the This Means War actress attached to play a supporting role, claims The Hollywood Reporter.
Witherspoon, who tied the knot with Jim Toth last March, is reportedly pregnant with her third child.
She previously revealed that she would love to have more children, sharing that she's "at a really good place" in her life.
Witherspoon has two children - Ava, 12, and Deacon, 8 - from her previous marriage to actor Ryan Phillippe.
Watch a trailer for This Means War below: