Jeong In Seong is the main vocalist of the boy group KNK. Along with bandmate Seungjun, he was a former Big Hit Entertainment trainee with the members of the boy group BTS. He was also an FNC Entertainment trainee. In 2015, together with his bandmates, he started hosting the reality show My Keunakeun Television on Naver TV Cast.
He is expected to enlist for his mandatory military service on February 8, 2022.