In October 2017, trainees from KQ Entertainment auditioned for the survival reality show MIXNINE. Jongho is one of the four boys that passed the audition. He ranked 27 in the MIXNINE Just Dance showcase but was eliminated in the tenth episode. His final ranking is number 43 Before debuting, Jongho was introduced as part of "KQ Fellaz", which is a pre-debut team of trainees under KQ. On October 24, 2018, Jongho debuted as a member of ATEEZ with the title tracks "Treasure" and "Pirate King".  

