Since the late 60s, Kirby has been seen on the small screen. He first garnered attention for several appearances as a fast-talking wheeler-dealer student who staged a banana-eating contest on "Room 222" and as an unstable, vengeful killer on an episode of "Kojak". He was Richard Castellano's rude son in the short-lived sitcom "The Super" (ABC, 1972). After nearly a decade absence, Kirby returned to TV in 1992 on "The Larry Sanders Show" (HBO).
Kirby made his Broadway debut replacing Kevin Spacey as a wannabe gangster in Neil Simon's Pulitzer Prize-winning play "Lost in Yonkers" (1991). Six years later, he was back in NYC, this time off-Broadway, playing Alan Zweibel in Zweibel's memoir-play about his friendship with comedienne Gilda Radner, "Bunny Bunny".