Everest is financing the movie, which also stars "One Tree Hill" and "The Tree of Life's" Tye Sheridan.
"Mud" "is the powerful, redemptive tale of a charismatic fugitive named Mud and his unlikely friendship with 14-year-old Ellis. Ellis is determined to help his new friend escape from both the law and some very serious bounty hunters in order to reunite Mud with his soul mate, Juniper."
McConaughey would play Mud, Sheridan would play Elllis and Witherspoon would play Juniper.
Jeff Nichols ("Take Shelter") wrote the movie and will direct.
Everest is fully financing. The company's Lisa Maria Falcone is producing with Sarah Green — who also produced "The Tree of Life." FilmNation Entertainment's Aaron Ryder also is producing.
"Jeff Nichols has written a beautiful story with rich characters learning valuable lessons through life-changing circumstances," Falcone said in a statement.