Kirby received his earliest onstage experience at Starlight Musical Theatre in San Diego. As a youth, he graduated from the littlest pickpocket in Oliver as a six-year-old, to the Emcee in Cabaret in his senior year in high school. Throughout grade school, he attended acting classes at San Diego Junior Theatre.

Kirby moved to Los Angeles to further his training with a scholarship to USC. He joined a student troupe from USC, traveling to the Fringe Festival in Edinburgh, Scotland to star as Joey in Pal Joey and Snoopy in the British premier of You’re a Good Man, Charlie Brown.

After leaving college, Kirby remained in Los Angeles finding work in film, stage, commercials, and voiceover. In 1993 he originated the roll of Bobby Child in the London premier of Crazy For You.

Following his stint in the West End of London, he moved his family to the New York area and began appearing on and off Broadway, in touring shows and regional productions, with an occasional TV appearance thrown in.