He has one brother, Jason.
Kirby started his acting career started in 1987, starring in a minor role in The Survivalist. He, however, didn't start seriously acting until 2001, after landing had another minor role in Smallville. From there, he appeared in a number of television roles, The Gifted, Famous in Love and Good Trouble, and movie roles, gaining a still-growing following. He will star in a recurring role in the third season The CW’s drama series Dynasty.
Kirby has been in a relationship with American actress Christine Ko since 2015.