The US Supreme Court rules unanimously to overturn Muhammad Ali's conviction. Three years later, Ali wins back the heavyweight championship.
In 1967, heavyweight boxing champion Muhammad Ali (shown in archive footage), a recent convert to Islam, is arrested due to his refusal to be drafted into the Vietnam War, claiming to be a conscientious objector due to his religious beliefs. Shortly after his arrest, he was stripped of his boxing license and his championship. He is convicted and sentenced to 5 years in prison, but is still free while the case is under appeal. In 1971, the appeal makes it way to the US Supreme Court.
The Justices agree to hear the case, but Justice Thurgood Marshall (Danny Glover) recuses himself due to a conflict of interest. The eight remaining Justices hear the case, but Chief Justice Warren Burger (Frank Langella) is under pressure from the White House and President Nixon to uphold the conviction. Under the guise of keeping the court unified, he essentially bullies his fellow conservative judges to vote to uphold Ali's conviction, making the final vote 5-3 in favor of upholding. Burger then appoints retiring Justice John Harlan (Christopher Plummer) to write the majority opinion, who in turn gives the job to one of his clerks, Kevin Kennedy (Benjamin Walker).
Kennedy, who believes that the law is on Ali's side, refuses to write the opinion the way Justice Harlan wants, and instead writes one that favors overturning Ali's conviction. He sites a precedent in which the Jehovah's Witnesses are allowed to be conscientious objectors due to their religious beliefs, and their arguments are identical to Ali's, except for the fact that he is a member of the Nation of Islam. That night, Justice Harlan reads what Kennedy originally wrote, and realizes that his clerk's opinion is the correct one. He also comes to believe the only reason Ali was convicted and all of his appeals were denied is because he is a Black Muslim. The next day, Harlan tells Kennedy he is officially changing his vote, making it a 4-4 deadlock.
Justice Harlan goes to his fellow judges that voted in favor of overturning Ali's conviction and tells them the only way this decision cannot be made to look political or racial is for a unanimous decision. The Justices then meet in the Chief Justice's office to try to convince the other four judges to change their vote. While deliberating, the judges note that the appeals court never specified why Ali's claims were rejected. With that knowledge, the three Justices who voted to uphold the conviction officially change their votes, leaving Chief Justice Burger as the lone dissenter. Knowing that a dissenting vote would make him appear to be a racist, Burger changes his vote, making it a unanimous 8-0 decision in favor of overturning Ali's conviction.
The movie ends three years later, with Ali defeating George Foreman to win back the heavyweight championship.