Jang Geun-seok began his entertainment career as a child model. He made his acting debut in the 1997 HBS sitcom Selling Happiness. In 2007, he won Best New Actor for Film at the 44th Baeksang Arts Awards for his work in The Happy Life. In 2009, his popularity soared to new heights after he starred in the hit SBS series You’re Beautiful. In 2010, he was named Most Popular Actor at the 46th Baeksang Arts Awards for the movie The Case of Itaewon Homicide. Also in 2010, he was nominated for an Excellence Award at the KBS Drama Awards for series Mary Stayed Out All Night. In 2012, he was once again recognized as Most Popular Actor at the 48th Baeksang Arts Awards for the film You’re My Pet. In 2015, he starred in dual roles in the KBS2 drama Love Rain, which was presold to Japan ahead of its premiere in Korea.

In 2015, Jang Geun-seok went on a hiatus in Korea after he was involved in a tax evasion controversy. He was later found not guilty. In 2016, he made a successful comeback with Mnet’s music survival show Produce 101. That same year, he starred in the SBS sageuk The Royal Gambler, in which he won a Top Excellence Award at the 2016 SBS Drama Awards.

Aside from his successful acting career, Jang Geun-seok also has an extensive music career in Asia. In April 2011, his first single titled Let Me Cry debuted at No. 1 on Japan’s Oricon chart. Jang Geun-seok then teamed up with DJ Big Brother to form the duo called Team H. In September 2011, they released their first Chinese mini album titled The Lounge H Vol. 1, which eventually reached platinum sales. In 2012, Jang Geun-seok again topped Japan’s Oricon chart with the release of his first full-length Japanese album titled Just Crazy.

In 2011, Jang Geun-seok was diagnosed with bipolar disorder. He began his mandatory military service on July 16, 2018, and was discharged on May 29, 2020. In August 2024, it was revealed that he had been diagnosed with thyroid cancer in October 2023 and had undergone a successful surgery in May 2024.