Kim was born in Seoul, South Korea. At the age of ten, Kim emigrated to the United States with her family.[citation needed] They lived in Staten Island, New York, one of New York City's five boroughs. She joined the middle school drama club in the 7th grade and performed in the musical My Fair Lady. Kim attended high school at the prestigious Fiorello H. LaGuardia High School of Music & Art and Performing Arts, a public high school located in Manhattan. From there, she went on to study drama at the London Academy of Performing Arts and later earned her drama degree at Boston University.

After graduation, Kim devoted herself full time to acting. She garnered several minor parts on MTV, in soap opera-style dramas on Abc and on the off-Broadway stage. In 1996, a Korean TV show filming in Manhattan called and persuaded her to return to her country of origin, to appear in the Korean TV drama A Gorgeous Vacation. This was followed by two other roles in Foreboding and the miniseries Wedding Dress. Then in 1997 she was offered a script for her debut film, Shiri (1999). Shiri was Korea's first blockbuster film and became the highest grossing film in the history of Korean cinema in 1999.

Over the next several years, she starred in five additional films. In July 2003, Kim signed a three-year contract with William Morris, an American agency representing Hollywood stars such as Halle Berry Salma Hayek Kevin Spacey, Sarah Michelle Gellar Lucy Liu Jackie Chan, and Reese Witherspoon.

Kim can currently be seen as the character Sun-Hwa Kwon in the television series Lost (2004).

In May 2006, Maxim named Kim #98 on its annual Hot 100 List. In October 2006 she was featured on the cover of Stuff, as well as a spread inside the magazine. Kim appeared in Maxim again in March 2007, where she was described as "the Korean Julia Roberts" in her native Korea.