Kim was born on 3 January 1987 and is the eldest of three siblings. She trained in martial arts as a child, and has attained third dan in Hapkido and second dan in Taekwondo. She also practices muay thai and boxing. She is known to have an interest in cars and motorcycles, speed racing, building computers, Sports such as soccer and baseball. Her IQ is known to be 141 (test taken during elementary school) and is ambidextrous.

Kim made her debut in an online beauty contest hosted by web portal Naver in 2004. Despite having little prior acting experience, she was cast of one of the three leads in the 2005 horror film Voice, a role which saw her nominated for "Best New Actress" at both the Blue Dragon Film Awards and Baeksang Arts Awards.

Kim auditioned for a part in the 2006 KBS drama series Hello, God, and after impressing Director Ji Yeong-soo with her "intense determination," was handed a leading role as confidence trickster Seo Eun-hye. During filming she expressed self-doubts, saying, "I used to cry two or three times everyday [sic] when the shooting began because I felt that I was a rubbish Actress," and with a tight schedule that allowed her less than two hours of sleep per day, was reported to have collapsed on set. Later that year, she appeared in MBC drama Over the Rainbow as aspiring pop singer Jeong Hee-su, a part which required her to sing and master difficult breakdance moves. Series Producer Han Hee complimented Kim, saying, "She is a bold Actress. She's very enthusiastic about her role with an almost perfectionist attitude." However, she caused some concern when she admitted to only eating one meal per day while filming the drama.

In February 2008, Kim was announced as the female lead in Park Chan-wook's Thirst, in a part that required numerous adult scenes with co-star Song Kang-ho. Kim felt that she learned much from working alongside Song, while Park commended her versatility in showing the different sides to her character. Thirst topped the South Korean box office during its opening weekend with over one million admissions, and was invited to the 2009 Cannes Film Festival where it won the Jury Prize. Richard Corliss of Time praised Kim's performance in the film, saying, "It's the lovely Kim, just 22, who is the revelation here. She can play — no, she can be — a creature of mute docility, then searching ardor, then explosive eroticism, then murderous intent. She is Lady Chatterley and Lady Macbeth in one smoldering package." The Hollywood Reporter's Maggie Lee was more critical, commenting, "[Kim's] high-pitched neurosis is sometimes grating, but for a relative newcomer, she keeps her continuous personality transformations in stride," while Kyu Hyun Kim of OhmyNews said, "Kim is stunningly sexy in both wilted-housewife and full-blown femme fatale modes, and throws all of herself into the role," but considered her "a bit too young and contemporary" for the role. She was a co-recipient of the Best Actress award at the 42nd Sitges Film Festival (shared with Elena Anaya for Hierro), and received further nominations at the Blue Dragon Film Awards, the Green Globe Film Awards, and the Baeksang Arts Awards.

Kim was reunited with Director E J-yong for Actresses, a low-budget film in which she and five other leading Korean actresses portray themselves at a special Vogue magazine shoot. Like her co-stars, Kim agreed to take part with no guarantee and shared writing credits. The film opened on 10 December 2009.

In 2011, Kim was to star opposite Eric Mun in KBS's action drama Poseidon, set for broadcast in July 2011. However they dropped out when production was halted after the Bombardment of Yeonpyeong incident in November 2010. In early 2012, she became the vocalist of a rock band, Ok Punk, which was also the title of the Mnet variety show starring the band.

Kim then dyed her hair pink for the 2012 comedy Over My Dead Body, which she said she greatly enjoyed filming, being a fan of the genre. This was followed by a leading role in the science fiction-thriller film 11 A.M., which was released in the second half of 2013.

Kim returned to television in 2013 in the KBS period epic The Blade and Petal set in the Goguryeo dynasty, her first TV drama in seven years. In 2014, Kim played a pickpocket in the jTBC cable comedy series Yoo-na's Street. Minority Opinion, her courtroom drama alongside Yoon Kye-sang and Yoo Hae-jin which had wrapped filming in 2013, was released in theaters in 2015.

In 2017, Kim starred in action thriller film The Villainess. The film was invited to the Cannes Film Festival, where it had its world premiere.

In 2018, Kim starred in military thriller The Discloser. The same year, she returned to the small screen in OCN's fantasy thriller drama Children of a Lesser God.