Being the second member to join H.O.T. after auditioning, Moon made his debut as a singer as the leader of the boy group. The group debuted with their first album, We Hate All Kinds of Violence in September 1996, which was accused of being plagiarized and lawsuits were placed against them. Despite their controversial debut, the group eventually rose to fame with their first hit, Candy and We Are the Future, which the latter won them a MTV award for Best International Video. During his time as part of the group, Moon composed and wrote music for the group and with fellow member, Jang Woo-hyuk, he often choreographed the group’s dance routine. Despite H.O.T.’s success, after releasing their last album, Outside Castle in September 2000, the group disbanded in May 2001.

After the disbandment of the group, Moon stayed on in S.M. Entertainment with Kangta, who was also part of H.O.T., and debuted as a solo artist. Moon attempted to establish a rock music career with his first album, Alone, but received criticism from the public. His second album, Messiah, was tinted with controversy as one of the songs, Media, was banned from all 3 major broadcasting stations in South Korea, for attacking mass media. After the release of his third album, Legend, in 2003, Moon released The Best: Soaring for a Dream, his last album under S.M. Entertainment and created his own company, PS Entertainment. After Moon released his fourth album, Triple X, he enlisted in the army in 2005.

Before entering the army, Moon had signed a contract with SidusHQ and during his time in the army, he hosted the KFN Korean Army Broadcast “Music Talk Show”, which received recognition from various Korean artistes. In 2008, Moon released his fifth album, Special Album, which included songs from H.O.T. previous albums. Moon released his first mini album, Last Cry, in 2009. In the same year, Moon appeared in sitcom Taehee, Hyegyo, Jihyun and took a break from the music scene.

Despite being absent from the music scene, Moon took up hosting in several variety programs such as, Immortal Songs: Singing the Legend, Mnet’s ‘Wide Celebrity News’ and other programs. In 2013, Moon released his second mini album, Begins, after being away from the music scene from 3 years. It was released on January 18, 2013.

In 2015, Moon signed an exclusive contract with KOEN Stars.

On November 25, 2016, Moon announced that he would be marrying fellow entertainer Park Hye-Kyeong, also known as Soyul of Crayon Pop. The wedding was held on February 12, 2017, in Seoul. The pair then welcomed their first child, daughter Moon Hee-yul, on May 12.