He is best known for starring in the Korean television dramas Beethoven Virus (2008), You're Beautiful (2009), Mary Stayed Out All Night (2010), Love Rain (2012), Bel Ami (2013), The Royal Gambler (2016), and Switch (2018).

Studying in New Zealand at the time, a role in the popular MBC sitcom Nonstop 4 brought him back to South Korea.

[5] In 2006, Jang debuted on the big screen in the Japanese horror film One Missed Call: Final where he played the role of a deaf boy.

[11] In 2008, Jang would go on to act in two more music-inspired projects with the film Do Re Mi Fa So La Ti Do,[12] and the MBC drama Beethoven Virus opposite Kim Myung-min, in which he played a trumpet player in an orchestra.

[13] He also starred in the KBS drama, Hong Gil-dong as the fictional brother of King Gwanghae who vies for Joseon's throne.

[19] In 2010, he starred opposite Moon Geun-young in the romantic comedy series Mary Stayed Out All Night.

[24] Jang then worked with TV director Yoon Seok-ho on the melodrama series Love Rain, in which he and costar Im Yoon-ah played dual roles in the 1970s and 2012.

[30] Jang filmed the reality show Three Meals a Day: Fishing Village with Cha Seung-won and Yoo Hae-jin, which was supposed to air in January 2015.

[38] That same year, Jang launched his directorial debut with the short film Camp, participating in the planning and directing stages in collaboration with director Yoon Hong-seung.

[39] He expressed his desire to be recognized as an actor in Korea again, saying that "You may be a Hallyu star, but without a domestic base, it can feel empty."

[40][41] Jang made a successful comeback in 2016 with Mnet's music survival show Produce 101, where 101 trainee girls competed against each other for their debut.

[43] Though it had lower viewership ratings, the series marked a turning point in Jang's career and allowed him to overcome his fixed image as a "pretty boy" and expand his acting roles.

[44][45] The same year, Jang directed the short film The Great Legacy, which centers on a man who is obsessed with finding a bankbook left by his unconscious father.

[47] In 2018, Jang returned to the small screen with the drama Switch - Change the World, playing double roles as a prosecutor and a con artist.

[59][60] In February 2013, Team H released their third album titled I Just Wanna Have Fun in both Japan and China, which consists of 12 electronic tracks.

[67] In 2014, Jang project band, Team H, released its third full-length album titled Driving to the Highway consisting of fourteen tracks.

[78] In August 2017, Jang dropped his 4th full-length album Voyage with a total of 14 songs, including three singles released in 2016.

He served as a social office worker following his diagnosis of bipolar disorder in 2011, which classified him as ineligible for active duty in the military.

[91] In 2016, Jang was appointed as a public ambassador for the media art exhibition “Van Gogh Inside: Festival of Music and Light".

[101] His fanclub also makes donations frequently,[102] such as to The Snail of Love, an organization that supports people with hearing impairments.