They appeared in regular live broadcasts of a series called Seventeen TV where they would show their practice performances to the general public. Their company, Pledis Entertainment, didn't have a lot of money so they were preparing for their debut in less-than ideal conditions. They also appeared on the reality show Seventeen Project: Big Debut Plan which ended with their long-awaited debut.
The group successfully debuted on May 26th with a live showcase and were the first male-group to debut with a one-hour showcase on a major broadcasting channel. They released two EP's (17 Carat and Boys Be) this year which landed them awards at the Golden Disk Awards, Seoul Music Awards, and Gaon Chart K-Pop Awards.
Their first studio album, Love & Letter, was released on April 25 which helped launch their international popularity. Not only were they successful on domestic charts, but in Japan as well. Their album's lead single "Pretty U" won them their first major win on a music show, and promotions started for their first tour. They also released their third EP, Going Seventeen.
Seventeen's fourth EP, Al1, was released on May 22 which peaked at No.1 in South Korea and the lead single, "Don't Wanna Cry", became one of the group's most popular tracks. The group also completed their first world tour on October 6 after performing in 13 countries across Asia and North America. On November 6, the group released their second studio album, Teen Age.
The group releases two more EP's (You Make My Day and You Made My Dawn) as well as their first Japanese single, "Happy Ending" which went on to receive a platinum certification from the Recording Industry Association of Japan. They also announced their world tour Ode to You and released their third studio album, An Ode. Following its release, the group won their first Daesang (the most prestigious Korean music award) for Album of the Year and was named best K-Pop album of the year by Billboard.
On April 1, Seventeen released their second Japanese single, "Fallin' Flower", placing first on Billboard's Japan Hot 100 Chart. Their seventh EP, Heng:aræ, sold one million copies in under a week making the group official "million sellers". On July 7, the album also charted at number one on the Oricon Weekly Album Chart for a second week, making Seventeen the first international male artist to do so since the Backstreet Boys over 12 years ago. Because of their immense popularity, HYBE Labels (BTS's Label) bought Pledis Entertainment for Seventeen.
Making their debut in US Television, Seventeen performed on The Late Late Show with James Corden as well as The Kelly Clarkson Show. On May 18, Seventeen announced that they would be partnering with Geffen Records and Universal Music Group for US and international distribution of their music. On October 22, the band released their ninth EP, Attaca, which sold two million copies making it the group's first double million-selling album.
In April of 2020, the group released their first film, Seventeen Power of Love: The Movie, in theaters across the world. On May 7 and 8, they held their Japanese Fanmeeting 'Hanabi' at Saitama Super Arena, their first in-person performance in the country in two and a half years since their Ode to You tour. They also completed their third world tour as well as performed at PMC's first-ever LA3C Festival in L.A.