Plummer, who is famous for his portrayal of a noble-browed patriarch in ‘The Sound of Music,’ will play the role of John Harlan II, the Washington Times reported.
Harlan II was among the justices who decided in 1971 whether Ali’s conviction for refusing to be drafted because of his Muslim-based objections should be upheld or overturned.
Plummer had earlier said that he doesn’t think retirement exists in the acting profession, and if someone retires, then something is very wrong with their career.
The 83-year-old actor added that he thinks that it is fun to be in the “weird, old, ancient, ancient profession of acting.”
The history-textured film puts the boxer’s quest to be recognized as a conscientious objector against Vietnam War service and the high court in the ring.
The film, which is directed Stephen Frears, also features Frank Langella as Chief Justice Warren Burger and Danny Glover as Thurgood Marshall, the sole black justice.