The group debuted on September 7, 2015, with the EP The Day, which peaked at No.2 on Billboard's World Album Chart a week following its release.

[6] JYP Entertainment initially announced the debut of a five-member band called 5Live, composed of Sungjin, Jae, Young K, Junhyeok, and Wonpil.

In 2014, the band began promotions by appearing on the fourth episode of Mnet's reality survival program Who is Next: Win and releasing a song titled "Lovely Girl" as part of the original soundtrack of the 2013 TV series Bel Ami.

Aside from performing songs from their debut album, the band also did multiple covers and played some unreleased materials of theirs.

On December 5, 2015, Day6 held their first overseas fanmeeting in Singapore at the Marina Bay Sands Convention Centre.

On February 27, 2016, JYP Entertainment stated that Junhyeok had departed from the band for personal reasons and terminated his contract with the company.

The music videos of their August, September, and October singles were a three-part story about high school friendship and love.

The album contained the previous releases from July to November, the lead single "I Like You", two sidetracks ("Better Better" and "I'll Try"), and the final versions of the B-sides from their debut EP The Day.

[28][unreliable source] Day6 made their official debut in Japan on March 14 with their first Japanese single, "If (Mata Aetara)".

[31] In April 2018, Day6 announced their first Japanese concert, Day6 1st Live in Japan 'The Best Day' on June 13 at Tsutaya O-East in Tokyo.

Which is composed of the band's previous Korean singles and three new-version tracks: "Congratulations" (English Ver.

Day6 went on their first world tour, titled Youth, subsequently performing in 24 cities in Asia, Australia, North America and Europe from June 22, 2018, to January 29, 2019.

[36] On January 10, 2019, the Day6 YouTube account announced that recruitment for their second-generation fan club would begin that month.

[42] The day before the album's scheduled release, JYP Entertainment announced that Day6 would be taking a temporary hiatus to focus on their health.

[43] Although Day6 is temporarily halting group activities, the band still released their EP The Book of Us: The Demon on May 11 at 6 p.m. KST.

[51] On March 8, 2021, Sungjin announced during his a V Live broadcast that he would be enlisting for his mandatory military service on the same day, having already recorded for the upcoming album.

[53] Due to Sungjin's military enlistment, the group decided that they would not be doing album promotions for The Book of Us: Negentropy.

[56] Dowoon debuted as Day6's third soloist with his first digital single, "Out of the Blue", on September 27, which is a duet with Song Heejin.

[57] On December 31, 2021, Jae announced via Twitter that he will be taking a hiatus from his promotions as a member of the band.

The same day, JYPE announced that he will be leaving the band and ending his exclusive contract with JYP Entertainment for personal reasons.

[67] On November 27, 2023, Wonpil became the fourth and last member to be discharged from military service as a Deckhand in the Naval Operations Command's 7th Mobility Squadron.

[79] Day6 made history by being the first K-band to ever perform at the Gocheok Sky Dome for their 2024 Christmas concert, The Present 2024.