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, the 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 Heun. In 2003, he released his second album, It's Real. To date, he has released four solo albums and has collaborated with many artists, including Se7en, M-Flo, and Masta Wu.