Lee Dong-gun made his entertainment debut in 1997 as a singer, but he would later gain fame as an actor, starring in television dramas such as Sweet 18, Lovers in Paris, and Stained Glass.

Lee took a break from acting in 2005, claiming he felt overwhelmed with his workload in both television and film. He later resumed his work in 2006, with Smile Again.

During a fan meeting event in Japan held on December 5, 2005, Lee announced the release of his first photo book which also included a making-of DVD, poster, and postcard. The success of Lovers in Paris along with promotions for his new film My Boyfriend Is Type B helped to increase his popularity in Japan

. Lee participated in the Hallyu Expo in Asia on Jeju island which commenced on November 28, 2006 and spanned a total of 100 days. This large scale event was intended to promote Korean culture across Asia and expected to bring in 150,000 tourists to stimulate the local economy. He also attended the sequel to the Hallyu Expo which was held in Japan titled FACE in Japan Premium Event. This two-day event from August 14–15, 2007, featured Korean celebrities with large fanbases and was intended as a cultural exchange program between Korea and Japan.

Lee released a 14-track album titled My Biography in 2008, his first full-length album in a decade. It included 6 Korean songs, 6 Japanese songs, and 2 instrumentals. It was first released in Japan before becoming available in Korea.

In December 2011, three months prior to the completion of his mandatory military service, Lee signed with talent agency Mask Entertainment. After the termination of his contract with Mask Entertainment, Lee signed with FNC Entertainment in November 2012.

In 2013, Lee was cast in the lead role for the time-travel romance Marry Him If You Dare. This was followed in 2015 by the titular role in cable series Super Daddy Yeol, which was based on the webtoon of the same name.