Kim began her career modeling in teen magazines, and made her acting debut in 1999. After a series of forgettable roles, she is best known for playing the youngest of the three sisters in sex comedy film Everybody Has Secrets, and the female lead in family drama I Am Happy.
In 2011 Kim replaced Han Chae-young in the Korea-China-Japan joint production Strangers 6, which tells the story of six individuals assigned by the highest level authorities of their respective countries to protect the three countries' joint economic area from being infiltrated by a hostile organization. Filming in Japan was delayed by the 2011 earthquake and tsunami, and the TV series aired on Japan's WOWOW TV and Korea's Channel A in 2012.
Kim first met actor-director Yoo Ji-tae in 2003 when they were models for a clothing brand, and their friendship turned into a romantic relationship in 2006. One of the few Korean star couples who openly admitted their dating status, they are very active in charitable organizations, and in 2011 were both appointed as honorary ambassadors for World Vision.
They announced their engagement in August 2011 (Kim reportedly turned down a movie role to prepare for her upcoming nuptials), and subsequently released pre-wedding photos. Their minimalist invitation was made from environmentally friendly paper and had the number 1,825 written on it, the exact amount of the days the two have spent together as a couple. They were married at the Shilla Hotel in Seoul on December 2, 2011. The date marked the couple's fifth anniversary together and was booked by Yoo one year in advance despite landing on a Friday – an unusual day for a wedding. The ceremony was officiated by the president of World Vision Korea; Yoo and Kim then donated a portion of their monetary gifts to the organization to help build an elementary and middle school in Myanmar. Kim gave birth to their first child, a son, on July 5, 2014.