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.
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.
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.
The courtroom scenes were filmed in an actual courtroom that the city let the filmmakers use. It was not a set.
Originally, Jonathan Demme was going to cast a comedic actor in role of Joe Miller, as he felt it would be a good counterbalance for Tom Hanks, who had already been cast and to give an audience the "it's okay" to watch a film about a gay man dying of AIDS. Demme had considered casting either Bill Murray or Robin Williams. But when Denzel Washington showed interest in the part, he gave the role to him instead, because Demme had wanted to work with Washington for the past few years.
Roger Corman: Mr. Laird, who testifies in court about how Andrew Beckett performed his duties at the law firm. Corman was a mentor to Jonathan Demme early in his directing career.
Tak Fujimoto: The cinematographer appears as a doctor in the hospital immediately following the birth scene.