Sacha Baron Cohen admitted he was "terrified" of having to do an American accent for the film. He had used a few different variations of the accent before for comedic reasons, but never for a dramatic role. He knew the real Abbie Hoffman had a unique voice, having a Massachusetts accent but also having gone to school in California, and was worried he would "sound wrong". Aaron Sorkin had to reassure him that the role was "not an impersonation, but an interpretation", which Baron Cohen claimed did not help much.
In the movie, Rennie Davis keeps a notebook with all the names of US soldiers that died in Vietnam during the trial. In real life, Rennie Davis wrote down the names of Vietnamese soldiers as well.
In regards to the film's timely subject matter in 2020, Aaron Sorkin described the film as being more about modern day than the 1960's. He explained that, "The script didn't change to mirror the times. The times changed to mirror the script."
In an appearance on NPR's Fresh Air, director Aaron Sorkin told host Terry Gross that he'd had to edit Judge Hoffman's character significantly to play down the true extent of his arrogance and irrationality on the bench, as documented in court records. Asked why he'd done this, Sorkin said he feared that to portray the judge's behavior as it actually was would strike the audience as implausible, resulting in the movie being dismissed as propaganda.
When Steven Spielberg was attached to direct, he was planning on meeting with Heath Ledger to discuss the role of Tom Hayden. Ledger passed away the day before he was scheduled to meet with Spielberg. Spielberg also wanted Will Smith to play Bobby Seale.