Jaejoong debuted with the South Korean boy group TVXQ in 2003. In October 2004, they released their first Korean studio album Tri-Angle, which featured the hit lead single Hug. In March 2006, they penetrated the Japanese market with the album Heart, Mind and Soul. In 2009, Jaejoong, along with his fellow TVXQ members Yoochun and Junsu, sued SM Entertainment over the supposedly unreasonable length of their exclusive contract. In 2010, the trio debuted as the South Korean boy group JYJ. In 2012, JYJ and SM Entertainment agreed to terminate all the contracts between the two parties and not to interfere with each other’s future activities. In January 2013, Jaejoong dropped his first solo mini-album I, which was followed by the release of his debut solo studio album WWW in October.

Jaejoong made his acting debut in the 2009 South Korean-Japanese film Heaven’s Postman, in which he starred with Han Hyo-joo. The following year, he landed his first small screen role in Fuji TV’s Hard to Say I Love You. In 2011, he starred in the SBS workplace romantic comedy Protect the Boss, which won him the New Star Award at the SBS Drama Awards. In 2012, he won Best New Actor at the MBC Drama Awards for his work in the fusion sageuk Dr. Jin. In 2014, he acted alongside Lee Beom-soo and Im Shi-wan in the MBC melodrama Triangle, which scored him a Top Excellence Award at the 7th Korea Drama Awards.

Jaejoong’s birth name was changed to Kim Jae-joong following his adoption when he was a young boy. In 2006, a man who claimed to be Jaejoong’s biological father filed a lawsuit against the idol’s adoptive parents for allegedly not going through the proper procedures before registering Jaejoong in their custody. The man later dropped the lawsuit. Jaejoong enlisted for his mandatory military service in March 2015 and was discharged in December 2016.