Wheesung began his career in 1999 with the short lived Korean boy band, A4. He left after the band's first album debut, citing musical differences between himself and the other members of the band. After being released from A4, he signed onto M Boat, a former sister company to YG Entertainment. He underwent a few years of vocal training under the label and released his first solo album Like A Movie in 2002. The album became very popular after receiving praise from many well-known artists, including Seo Taiji and Shin Seung Hun. In 2003, he released his second album, It's Real. It proved to be as popular as his first, making him the best selling artist of 2003 in Korea. Unlike his debut album, It's Real wasn't restricted to R&B and it included different musical elements like pop and hip-hop. Wheesung left YG Entertainment after his contract expired in March 2006. He signed a new contract that is reportedly worth 1.5 million won with his new company Orange Shock Agency.
Wheesung has collaborated with many artists. In late 2008, Wheesung has collaborated once again with Lee Hyori who featured as his girlfriend in his music video of "별이 지다.." (Fading Star) in the "With All My Heart and Soul" album. In 2009, Wheesung seeks help from producer Lee Hyun-do, they will collaborate to produce the new album which the release date has been set in August 2009.
In April 2009, Wheesung is the MC/host of a new Mnet TV show called "Pre Star-1 Show. This show gives opportunities for new talented singers to introduce themselves, a platform for them to reach out to more fans. Every month about nine or ten teams will be introduced on Mnet.com and the team which receives most response from the netizens will be chosen onto the show. The chosen team/singer will also be given the chance to perform with popular stars. Wheesung's Pre-Show 1 Show’ started airing on 24 April on Mnet Cable Channel.
Wheesung had participated in several Kpop concerts in Los Angeles, California, which include the Hollywood Bowl, and the Victory Concert. On June 19, 2009, Wheesung and Lena Park held a concert in Los Angeles Disney Concert Hall. After the concert, Wheesung planned to stay in Los Angeles for a month to work on his new album with producer Lee Hyun-do. The new album will go back to the r&b/hiphop style similar to "With Me" and "Incurable Disease". The new album is set to be released in August 2009. Wheesung also claimed in an interview that he wants to visit Pink's Hot Dogs while in LA. On June 27 and July 4, Wheesung performed at "Insomnia Concert" and club Le Cercle in LA. On July 11, he performed at the HALO nightclub in Hollywood.
In June 2009, Wheesung changed his label again from Orange Shock to POP/UP Entertainment, which houses stars like JK Kim Dong Wook and group M to M. Wheesung has decided to change his label because former producer, Park Gun Tae, concentrated more on producing and working by himself. Wheesung gave thanks to Park Gun Tae for his growth as an artist and hopes to learn from him as a little brother, no longer as an artist under a producer.
On 11 July 2012 Wheesung was granted a 9 nights, 10 days temporary leave from the army to undergo surgery for a herniated disc as well as other medical conditions such as bilateral shoulders dislocation, psoriasis and alopecia.