Kim Sung Hyun was a contestant on 2016 reality boy group unit survival show BOYS24. He was a lead rapper and member of Unit Black, the first promotional unit of BOYS24. He is a vocalist, rapper, maknae, and member of IN2IT, the final group of BOYS24. He is a contestant on 2019 boy group survival reality show Produce X 101.

He was included in Unit Red during the BOYS24 survival show and eliminated in the final stage (episode 8), but revived from fans vote. He was selected as one of the BOYS24 group members and added to Unit White (first generation). This Unit line-up performed regular shows in their own concert hall from September 22, 2016, to March 19, 2017. On November 20, 2016, the group announced that they would perform with the new line-up that was called Collabo line-up. Sung Hyun was included in Collabo white that performed from December 7, 2016, to March 14, 2017.

On March 5, 2017, the group announced new units. He was one of the members with the highest points voted by fans and chosen as the leader of Unit Purple (second generation). This new units line-up performed from March 24, 2017, to August 6, 2017. At the same day, he was also selected from the 'BOYS24 The 1st Semi-Final' concert in 5th place based on fans vote to promote as Unit Black for three months.

On August 12, 2017, he was selected from 'BOYS24 The Final' concert in 4th place based on fans vote and announced as one of the final group members. He debuted as a member of IN2IT under MMO Entertainment on October 26, 2017.

After training for seven years and three months and performed over 400 times on stage, he made his appearance as a contestant under Stone Music Entertainment on Produce X 101.

On September 5, 2019 MMO Entertainment announced Kim Sunghyun’s departure from IN2IT due to personal reasons.