1ST.ONE consists of six members: Ace, Alpha, J, Jayson, Joker, and Max. They were all FIRST ONE trainees previously revealed to the public through their social media teaser photos and videos.

Prior to their official debut, 1ST.ONE has already performed alongside biggest K-Pop artists such as TWICE, Monsta X, Red Velvet, NCT, TXT, Girls’ Generation’s Taeyeon, and many more at the High 1 Seoul Music Awards (SMA) in January 2020. SMA, one of the most prestigious music awards shows in South Korea, chose 1ST.ONE to be the Philippines’ representative artist to perform as opening act for the show. This made them the very first Filipino artists to ever perform in the ceremony.