2018–2020: Under Nineteen and 1THE9
On October 25, 2018, Jeong Taek Hyeon was introduced as a contestant of Under Nineteen with his moving poster. The poster revealed that he was a part of the rap team. He finished in fifth place, thus becoming a member of the project group 1THE9.
On April 13, 2019, the group officially debuted with the mini album XIX.
- Under Nineteen (MBC, 2018-2019) - contestant