Remar, who starred in the original Broadway production of Bent, will play Gibby, a physician and old friend of Pete (played by Tim Daly).
Stewart will appear in the season premiere as a man named Kevin, who is willing to give a kidney.to his estranged brother, but may not be fit to be a donor because of his mental state. He recently starred on stage in Voice Lessons opposite Laurie Metcalf and the Geffen Playhouse's production of Matthew Modine Saves the Alpacas. He is best known for his work on the NBC sitcom Third Rock from the Sun.
Private Practice stars stage veterans Kate Walsh, Taye Diggs, Audra McDonald, and Amy Brennenman.