Already before thier debut, the most members were active in the industry. Chaeryeong was a contestant on K-pop Star 3 in 2013. In 2015, she went to compete in JYP survival show Sixteen in 2015, however, she failed to become a member of the winning girl group, Twice. Ryujin was a contestant on JTBC's survival show Mix Nine. In 2018, she placed first for girls. In the final competition of the show where it was between a team of nine boys and a team of nine girls, the boys team won. Yeji was a contestant on SBS' The Fan but was eliminated in episode 5. All of the members, with the exception of Lia, appeared in Mnet's reality show Stray Kids as a project group against the boy group Stray Kids in 2017.

On January 21 2019, JYP Entertainment announced they would be debuting a new girl group, being the first girl group from the label since Twice's 2015 debut. On the same day, the group's official YouTube account was created and the label's official channel shared a video trailer unveiling the five members.
On February 12, the group released their debut single album, "It'z Different", with its lead single "DALLA DALLA". The song incorporates elements from EDM subgenres, such as future house and bass house. Its empowering lyrics have been well received by the audience. The music video surpassed 14 million views within 24 hours of its release, with Youtube confirming that DALLA DALLA had a total of 17.1 million views for its first 24 hours since publishing.
ITZY's debut EP, titled IT'z ICY was released on July 29, 2019 along with an accompanied music video for it's lead single titled "ICY".
ITZY started the year 2020 with their showcase tour in the United States, on January 17 in Los Angeles and finished on January 26 in New York City.
On March 9, 2020, ITZY made their comeback with their second mini album, "IT'z ME" and its title track "WANNABE".
On August 17, 2020 ITZY made their comeback with their third mini album, "Not Shy" and it's title track "Not Shy".
On December 25, 2020, ITZY revealed the tracklist for their English debut album "Not Shy" (English Ver.). It was released on January 22, 2021, and includes English versions of all their title tracks (DALLA DALLA, ICY, WANNABE and Not Shy). On March 12, ITZY released the digital single "Trust Me" (MIDZY), a song dedicated to their fans, as part of their first global livestream event.
On April 30, 2021, ITZY made their comeback with their fourth mini album, "GUESS WHO" and it's title track "마.피.아. In the morning".
On the midnight of August 13, ITZY released a comeback poster for their first full album "CRAZY IN LOVE" to be released. On September 24, ITZY released their first studio album "CRAZY IN LOVE" and its lead single "LOCO".
On June 2 2022, ITZY announced they will be coming back with their fifth mini album, "CHECKMATE", on July 15. Furthermore, the group will kick off their first world tour, also entitled "CHECKMATE", with two nights of concerts in Seoul on August 6 and 7, before heading to the United States.