Kim was born in Busan, South Korea, the son of mother Jung Kim and father Dr. Doo Tae Kim, and moved to the United States with his family when he was two years old. He grew up in the city of Bethlehem, Pennsylvania. Kim was educated at Freedom High School, a public school in his home city of Bethlehem, Pennsylvania. He graduated from Haverford College in Pennsylvania with a Bachelor's degree in 1990, and earned an MFA from NYU's Graduate Acting Program in 1996.
After graduation, Kim made a name for himself playing numerous roles in a wide variety of television programs. He appeared in CSI: Crime Scene Investigation as a treasury agent as well as episodes of Star Trek: Voyager, Star Trek: Enterprise, Charmed, The Shield, Seinfeld, NYPD Blue and ER. He was a regular on the short-lived Babylon 5 spin-off Crusade and had recurring roles on Angel and 24. He also portrayed Dr. Tsi Chou in a 2008 miniseries based on the acclaimed Michael Crichton novel The Andromeda Strain. His film credits include a small part in Spider-Man 2 as a scientist working in Doctor Octavius' laboratory, and Crash, the 2005 Best Picture Academy Award winner. He also had minor roles in films such as The Jackal, For Love of the Game, Hulk and The Cave. From 2004 to 2010, Kim served as a regular cast member on the ABC series Lost in which he played Jin-Soo Kwon, a lowly Korean fisherman-turned-hitman who crashes onto a mysterious island with his wife, Sun-Hwa Kwon (Yunjin Kim). Since the role required him to speak exclusively in Korean, Kim said he was forced to quickly relearn the language, which he had not spoken with any great frequency since high school. He would go on to play the character up until the 2010 series finale. Throughout the show's run, Kim, along with his fellow cast members, received numerous accolades, including a 2006 Screen Actors Guild Award for Best Ensemble.
Kim was individually honored with an AZN Asian Excellence Award, a Multicultural Prism Award and a Vanguard Award from the Korean American Coalition, all for Outstanding Performance by an Actor. Kim was also named one of People Magazine's "Sexiest Men Alive" in 2005. In February 2010, shortly after Lost's conclusion, it was announced that Kim would join the CBS reboot Hawaii Five-0 playing Chin Ho Kelly, the role originally made famous by actor Kam Fong. Kim was the first actor to be officially cast on the show. That series premiered on September 20, 2010 to strong ratings and solid critical acclaim. Kim departed the show in late June 2017 prior to the eighth season due to a salary dispute with CBS. Kim had been seeking pay equality with co-stars Alex O'Loughlin and Scott Caan, but CBS's final offer to Kim was 10–15% lower than what O'Loughlin and Caan make in salary. Kim co-starred in The Divergent Series: Insurgent, the sequel to 2014's Divergent, playing Jack Kang, the leader of the Candor faction. In addition to acting, Kim made his directorial debut with the Hawaii Five-0 Season 5 episode, "Kuka'awale."