Krystal was born in San Francisco, California, where her family from South Korea settled in the 1980s. During a family trip to South Korea in early 2000, when Krystal was five years old, she and her older sister Jessica were spotted by talent agency S.M. Entertainment, which earned her a cameo appearance in Shinhwa's "Wedding March" music video. The agency saw potential in both Krystal and her sister and offered them singing and dancing lessons, opting to professionally train them in a singing career. However, the offer was turned down by her parents, reasoning that Krystal was too young. Therefore, her parents at first only allowed her older sister to join the agency, who debuted as a member of girl group Girls' Generation in August 2007.
In 2002, Krystal began appearing in television commercials. She first appeared in a Lotte commercial with Korean actress Han Ga In. In 2006, her parents allowed her to join SM Entertainment, and the agency enrolled her in dance classes, including hip hop and jazz.
A teaser trailer of f(x) was released via YouTube on August 24, 2009. The group's debut digital single "LA chA TA" was released on September 1, followed by a 40-second teaser of the corresponding music video revealed on YouTube. The group debuted on September 2 in a showcase specifically designed to introduce the group, in an event held at the Samseong-dong Fashion Center. On September 5, f(x) had their first broadcast performance on MBC's music show Music Core. In 2010, she released a solo song named "Melody" accompanied with a music video.
In 2010, Krystal appeared on Let's Go Dream Team 2, where she broke a high jump record that had been set on the show 10 years ago. She now holds the Korean women's high jump record of 1.95m.
In 2010, she was given a minor role in the TV sitcom More Charming by the Day. She was also a host of The M-Wave with fellow artist Thunder from MBLAQ.,.
In 2011, she competed on the SBS skating reality show Kim Yuna's Kiss & Cry. During the episode that aired on August 14, 2011, Krystal and her skating partner Lee Dong Hun won the competition, earning them the opportunity to skate at Kim Yuna's ‘Samsung Galaxy★Hauzen All That Skate Summer 2011‘ ice show.
Krystal also appeared in High Kick!, a Korean television series, portraying the role of Ahn Soojung in the third season of the popular daily series.