Kim grew up in California, United States. Kim first appeared in the "2002 Survival Audition HeeJun vs. KangTa Battle of the Century" along with JYJ's Xiah and Super Junior's Sungmin and Eunhyuk. He then became a lead vocalist for the band TRAX along with three other members Rose, Attack and X-Mas. The band has released a full-length album (Cho-u; 2006) and two mini-albums (Let U Go and Oh! My Goddess, both in 2010) to varying success. In 2010, TRAX became a special guest for Super Junior's third Asian tour, Super Show 3 in some tour dates, performing on the bridge of the song Don't Don. In November 2010, Kim has participated with SM labelmates Super Junior's Kyuhyun, SHINee's Jonghyun and new member Jino for the ballad project group S.M. the Ballad. The quartet had released a five-track album entitled Neomu Geuriwo (Miss You) on the same month and sold a total of 23,000 copies by the end of 2010 according to the South Korean Gaon charts, being the 66th best-selling Korean-language physical release in South Korea.
TRAX released their third EP, Blind on November 10, 2011. They will have their comeback performance on M!Countdown on the same day.
Kim had his acting debut in the 2009 drama series Romance Zero. He also participated in musicals such as Brothers Were Brave and Rock of Ages in 2010. He has also starred in the musical The Three Musketeers, alongside labelmates Super Junior's Kyuhyun and CSJH The Grace's Dana. He was cast to act alongside Super Junior's Sungmin in the 2010 KBS drama President. He plays the role of Sungmin's half-brother.