The moment when Mary Steenburgen's character says that she hates the case was improvised in the moment, when the actress expressed her hate towards her role after shooting the mirror scene and Jonathan Demme encouraged her to incorporate it into the role, so the woman would seem more human.
Tom Hanks had to lose almost thirty pounds to appear appropriately gaunt for his courtroom scenes. Denzel Washington, on the other hand, was asked to gain a few pounds for his role. Washington, to the chagrin of Hanks, who practically starved himself for the role, would often eat chocolate bars in front of him.
Director Jonathan Demme wanted people not familiar with AIDS to see his film. He felt Bruce Springsteen would bring an audience that would not ordinarily see a movie about a gay man dying of AIDS. The movie and the song "The Streets of Philadelphia" did a great deal to increase AIDS awareness and take some of the stigma off the disease.
According to a 1994 Entertainment Weekly profile of Ron Vawter by Stephen Schaefer, Jonathan Demme had to convince TriStar Pictures to hire Vawter to play Bob Seidman. TriStar wanted Demme to hire someone else because Vawter was HIV-positive and the insurance company covering the film refused to extend coverage to him. Demme managed to convince TriStar to allow the hiring of Vawter anyway, both because Vawter was the actor that Demme wanted, and because refusing to hire an actor because of his HIV-positive status would have been particularly ironic in the context of a movie that is premised on the injustice of a lawyer being fired because he is HIV-positive.
The courtroom scenes were filmed in an actual courtroom that the city let the filmmakers use. It was not a set.
Tak Fujimoto: The cinematographer appears as a doctor in the hospital immediately following the birth scene.
Roger Corman: As Mr. Laird, who gives his views in court to Joe Miller, on how Andrew Beckett performed his duties at the law firm. Corman was a mentor to Jonathan Demme early in his directing career.