2018–2020: Produce 48 and Iz*One
From June 15 to August 31, 2018, Jang represented Starship Entertainment alongside An Yu-jin and Cho Ka-hyeon on the girl group survival reality television show Produce 48. She eventually placed first and debuted with Iz*One.[10]
Iz*One's Korean debut extended play (EP) Color*Iz was released on October 29, 2018, under the label Off the Record, with "La Vie en Rose" serving as lead single.[11] Both the EP and its lead single received immediate commercial success, leading the group to win the New Artist of the Year award at several shows, including Golden Disc Awards and Seoul Music Awards.[12]
The group's Japanese debut single, "Suki to Iwasetai", was released on February 6, 2019, under UMG's EMI Records subsidiary.[13] Along with the group's Japanese debut promotion, Jang was selected alongside the Japanese member Sakura Miyawaki to center a collaborative performance between Nogizaka46, Keyakizaka46, and AKB48 at the FNS Music Festival.[14] In September 2019, Jang made her runway debut at the 29th Tokyo Girls Collection's 2019 Autumn/Winter fashion festival at Saitama Super Arena.[15] She also appeared at the Kitakyushu edition of the festival later that year.[16] On February 17, 2020, Iz*One released their first Korean-language studio album Bloom*Iz, on which Jang co-wrote the track "Dreamlike." The song was named by music webzine Beats Per Minute as the 19th best song of 2020, with critic J.T. Early praising the song for its "bright and irresistible force".[17]

2021–present: Ive, Music Bank, and solo activities
After Iz*One's disbandment on April 29, 2021, Jang returned to Starship Entertainment as a trainee along with group mate and labelmate An Yu-jin. In September 2021, Jang was announced as the new host of the program Music Bank with Enhypen's Sunghoon.[18] For their performance on the program, they were awarded with the Best Couple Award at the 2021 KBS Entertainment Awards.[19] On October 12, she and Leeteuk were chosen to host the 2021 Asia Artist Awards, which would be held in December of that year.[20] On November 4, 2021, Starship Entertainment revealed Jang as one of the six members in their new girl group Ive.[21][22] On December 1, 2021, Jang officially debuted as a member of Ive with the release of their single album Eleven, led by the single of the same name.[23]
In September 2022, Jang attended the 2022 Paris Fashion Week as an ambassador for luxury fashion brands Miu Miu and Fred Joaillier.[24][25] That same month, her contract as the host of Music Bank was extended.[26] On December 13, Jang hosted the 2022 Asia Artist Awards with Leeteuk.[27] Three days later, she also hosted the 2022 KBS Song Festival with Na In-woo and Kim Shin-young.[28] In January 2023, Jang stepped down as Music Bank host after sixteen months in the role.[29]

Ive released their first studio album, I've Ive, in April 2023, on which Jang wrote two tracks, "Mine" and "Shine with Me".[30] On August 18, she hosted the Friday night first concert of KCON LA 2023.[31] A month later, Jang was announced to be the host for the 8th Asia Artist Awards with co-hosts Kang Daniel and Sung Han-bin, which would be held in December of that year.[32] She was named by influencer marketing platform Lefty as the 13th top influencer of Paris Fashion Week, with her appearance generating an estimated media value of $3 million for Miu Miu.[33] On October 13, Ive released their extended play, I've Mine, on which Jang wrote the track "OTT".[34] On November 26, it was announced that Jang would be hosting the 2023 KBS Music Bank Global Festival alongside Rowoon on December 15.[35]

On April 29, 2024, Ive released their second extended play Ive Switch, on which Jang wrote the track "Blue Heart", her fourth work as a solo lyricist.[36] In an interview with Nylon, she stated that the song was inspired by her experiences in the entertainment industry, where women faced hyperscrutiny from media and fans.[37] In September 2024, Jang was announced to be the host for 9th Asia Artist Awards, which would be held in December of the same year, with co-host Sung Han-bin.[38] It was also confirmed in November 2024 that Jang would be hosting the 2024 KBS Music Bank Global Festival alongside Zico and Kim Young-dae on December 20.[39] This marked her third consecutive year of hosting the KBS Year End Festival.[40]

In April 2025, Jang was announced to be the host for 10th Asia Artist Awards, which would be held in December of the same year, with co-host Lee Jun-ho. This is her 5th consecutive years hosting the award, since 2021.[41]