“Dallas Buyers Club” helmer Jean-Marc Vallee is helming the pic.
Pic is based on the Cheryl Strayed book and chronicles a woman who undertakes a 1,100-mile solo hike as a way to recover from a recent catastrophe.
Witherspoon is also producing along with her producing partner Bruna Papandrea through their Pacific Standard banner.
The part marks Sadoski’s first major film role since breaking out in “The Newsroom,” which just wrapped its second season. He is repped by UTA and Industry Entertainment.
News was first reported in the Hollywood Reporter.