Kim Jae-kyung debuted with the South Korean girl group Rainbow in 2009 with the extended play Gossip Girl. They have two studio albums under their belt, namely Over the Rainbow released in Japan in 2012 and Rainbow Syndrome released in two installments in South Korea in 2013. The group disbanded in 2016 but made a comeback in 2019 to mark their 10th anniversary.

In 2012, Kim Jae-kyung was cast as one of the main characters in the JTBC drama special Monster. In 2015, she took on the female leading role in the web series Noble, My Love, opposite Sung Hoon. In 2018, she joined OCN’s Life on Mars. That same year, she became part of the main cast of the MBC series Bad Papa, which won her Best Supporting Actress at the MBC Drama Awards. In 2019, she starred in the SBS romantic comedy The Secret Life of My Secretary, which earned her a Best Supporting Actress nomination at the SBS Drama Awards. In 2021, she appeared in tvN’s The Devil Judge.

Kim Jae-kyung attended Dongduk Women’s University’s design department. Her brother Jaehyun is a member of the South Korean rap rock band N.Flying.