Lee was born in Seoul, South Korea. His middle name, Kyson, from the first letters of his parents' surname "k" & "y", and the word "son", means "Child of the Spirit." Lee moved with his family to New York City at the age of 10, where he later attended the Bronx High School of Science. He studied communications at Boston University and the New England Institute of the Art.

In the summer of 2001, he moved to Los Angeles. There he began training in jazz singing, musical theater, and acting.

He performed improv with L.A. based Asian-American improv troupe 'Room To Improv', and studied comedy at The Groundlings, Upright Citizens Brigade, and I.O. West in Los Angeles.

In his first-ever television audition, he landed a guest-starring role on the CBS television drama JAG and has been a working actor ever since.

Lee appeared at the Miss Universe competition held in Mexico City (where he was incorrectly introduced as a Japanese American). His question to a contestant—who was coincidentally Miss Korea 2007 Honey Lee—was "If you had a superpower, what would it be and why?"

Lee's most famous role is that of Ando Masahashi on the NBC drama series Heroes. A recurring character in the first season, he was upgraded to the main cast for the second.

• Destiny (2009) — Gates
• Hardbreakers (2009) — Evan Stone
• Then There's the Afterlife (2009) — Sung
• How to make Love to a Woman (2009) — Aaron
• Termination Shock (2009) — Lei Chen
• Akira's Hip Hop Shop (2009) — Akira Kubota
• Do Over (2009) — Mike Lee
• The Roel (2009) — Ansel
• Doesn't Texas Ever End (2009) — Rick
• White on Rice (2009) — Tim Kim
• Necrosis (2008) — Jerry
• Shutter (2008) — Ritsuo
• Moola (2008) — Jimmy Woo
• Asian Stories (Book 3) (2006) — Jim Lee
• Ghost Hunters: Point of Contact (2006) — Dr. Ken Shin
• Big Dreams Little Tokyo (2006) — Murakami
• Las Vegas — Joon Ho Park (2007)
• Heroes — Ando Masahashi (2006 - )
• On the Rocks (2006) — Donald Park
• Heist (2006) — Universal Studio Guide
• Doberman (2005) — Johnny
• Snapdragon (2005) — Hyun
• Bunny & Clydo (2005) — Clydo
• The West Wing (2004) — Chinese Translator Zheng
• Threat Matrix (2004) — Vargas Killer
• All About the Andersons (2003) — Josh
• JAG (2003) — Lieutenant Pak (1 episode, 2003)