The True Blood star is set to play prosecutor John Fogelman in the feature film about the West Memphis Three, according to Deadline.
Helmed by Chloe director Atom Egoyan, the movie will chronicle the wrongful conviction and imprisonment of teenagers Jason Baldwin, Damien Echols and Jessie Misskelley for the murders of three young boys in 1993.
Based on the 2003 book Devil's Knot: The True Story of the West Memphis Three, the film will also star Colin Firth and Reese Witherspoon.
Moyer will reportedly begin work on the film immediately to accommodate shooting on the next season of True Blood.
Devil's Knot is expected for release in cinemas next year.