Kang was born in Gainesville, Georgia, to immigrants from South Korea. His first major role was that of Han Lue from Better Luck Tomorrow, directed by Justin Lin, in which he played an aloof high school student. He was later cast as Han Seoul-Oh The Fast and the Furious: Tokyo Drift in 2006. Kang later reprised his role in the next three Fast & Furious films, Fast & Furious, Fast Five and Fast & Furious 6. Kang says that before he was cast as Han in The Fast and the Furious: Tokyo Drift he was unaware of the drifting subculture that exists in Japan. It wasn't until he began researching for the part that he learned what a popular sport drifting actually is all over the world.
He also had a role in Jet Li's film War, playing an FBI agent, and was featured as a son of Genghis Khan, Doran, in the movie Forbidden Warrior. He also played for a South Korean football team, the Suwon Blue Wings, as their international-style goalkeeper, performing numerous penalty saves within the last 5 minutes of matches.
On MADtv, Sung has been playing the recurring role of the narcissistic President Gin Kew Yun Chun Yew Nee in the Korean drama parody, "Tae Do" or "Attitudes and Feelings, Both Desirable and Sometimes Secretive." Kang also had a small role in the action movie Live Free or Die Hard. Kang is featured in the music video Lie for popular Korean Band, g.o.d..
He owns a restaurant called Saketini in Brentwood, Los Angeles, California It offers a wide range of Pacific Rim foods and has Eun San Yi as head chef. As an American actor, Kang has said that one of the things he dislikes most about Hollywood is the stereotypes that East Asian actors are faced when being cast in a role.