His first appearance was through Orange Caramel's "Bangkok City" music video, and was first introduced toward public in the show Hello Counselor by Kahi together with Baekho.

[4] Jonghyeon also served as a back up dancer for After School Blue's "Wonder Boy" music video and live performances, together with NU'EST members and Seventeen's S.Coups.

[9][10] On June 27, 2018, Kim was confirmed as a member of Mnet's new romance reality show Love Catcher [ko].

[15] It was announced on February 28, 2022, that NU'EST's exclusive contract with Pledis Entertainment will expire on March 14, 2022, and Kim (alongside members Aron and Ren) will leave the agency, therefore concluding their 10-year career as a group.

In addition, he would also reveal the EP details and perform the tracks before its release during the "Sparkling Eternity" fan concert on December 29 to 30, 2023.

[22] On August 18, 2024, Kim held a live broadcast announcing that he would have to fulfill his military mandatory service as an active duty soldier on September 23.