Kim Sung-joo is a South Korean singer and actor. Kim debuted as a member of South Korean-Chinese band UNIQ in 2014. He graduated from Anyang Arts High School and is enrolled in the Broadcasting Entertainment program at Global Cyber ​​University. He made his television debut in the romantic Chinese drama Magical Space-time and his film debut in MBA Partners. He is best known for his supporting roles in Live Up to Your Name and My Secret Terrius.

In 2014, YG Entertainment began a project to launch a new boy group composed of trainees who had been learning between 2-5 years. They brought Yuehua Entertainment (위에화엔터테인먼트) to co-manage the group, but in the end, Yuehua kept full control of it.

He made his debut in October 2014 as UNIQ's Korean leader and main vocalist with their single, "Falling in Love", released in both Mandarin and Korean. The group also provided the OSTs for the Chinese version of the movies "TMNT" and "Penguins of Madagascar".

After releasing two singles in April 2018, UNIQ went on an indefinite hiatus, and while they have never disbanded, they have not released any new material since then.

He enlisted for his mandatory military service on March 9, 2020, and was discharged on September 16, 2021. After being released, he left South Korea and is now working as an actor in China.