As previously reported, Tony Award winners Christopher Plummer (Cyrano, Barrymore) and Frank Langella (Seascape, Fortune's Fool, Frost/Nixon) have been cast in the film directed by Stephen Frears, which "details the legal fight between Ali and the U.S. government when the fighter became a conscientious objector to the Vietnam War."
Walker is in negotiations for the role of Kevin Kennedy, a Supreme Court clerk. Plummer has signed on to play Supreme Court judge John Marshall Harlan, and Langella will play Chief Justice Warren Burger. According to Variety, the film will utilize actual footage of Ali and not cast an actor to play him.
Frank Doelger, Tracey Scoffield, Jonathan Cameron and Frears are the executive producers of the film, which features a screenplay by Shawn Slovo.
Walker has been seen on Broadway in Bloody Bloody Andrew Jackson, Les Liaisons Dangereuses and Inherit the Wind. His film credits include "Abraham Lincoln: Vampire Hunter," "The War Boys," "Flags of Our Fathers" and "Kinsey," among others.