Jun first became well known as a commercial model and as a TV actress. Although she made her film debut in the little-watched White Valentine in 1999, it was not until later in the year when she was featured in a commercial for Samsung My Jet Printer that she became a popular sensation. The dancing and attitude expressed in the ad made Jun into an icon for Koreans in her late teens and early twenties.

The following year, Jun made her first well-publicized film appearance in late 2000 with Il Mare, a handsomely shot melodrama set on Ganghwa Island. The film did respectably well at the box office (despite opening on the same day as blockbuster Joint Security Area) and solidified her status as a star.

Jun’s breakout film was comedy My Sassy Girl, a tale of a gullible college student and his slightly unhinged girlfriend, which became a huge blockbuster hit both in Korea and throughout Asia. The film became the highest grossing Korean comedy of all time in Korea and also spent two weeks at No. 1 in Hong Kong, launching Jun into pan-asia stardom as one of the biggest Hallyu star in the Chinese-language market. The huge success of My Sassy Girl also solidified Jun’s domestic popularity, and she was given the title of the “Nation’s First Love” by the media for her natural beauty and charming image. Jun’s growing popularity resulted in many companies requesting her endorsement. Consequently, Jun was labelled as the “CF Queen” in South Korea. She also won as Best Actress at the 2002 Grand Bell Awards.