Jang Hyuk made his acting debut in the 1997 SBS drama Model. In 2002, he starred in the SBS romantic comedy Successful Story of a Bright Girl, opposite Jang Nara. The series was a huge success, recording a peak viewership rating of 42.6 percent. It also won him a Top Excellence Award at the 2002 SBS Drama Awards. In 2004, he starred opposite Jeon Ji-hyun in the film Windstruck, which ranked the 8th best-selling Korean film of that year. In 2010, he headlined the sageuk drama Chuno, which earned him the Daesang at the KBS Drama Awards. His work in the series also gave him a Best Actor nomination at the 39th International Emmy Awards. In 2014, he reunited with his Successful Story of a Bright Girl co-star Jang Nara in Fated to Love You, which is a remake of the Taiwanese series of the same name. He won a Top Excellence Award at the 2014 MBC Drama Awards for his performance in the series. In 2017, he won another Top Excellence Award for the 2017 MBC weekend series Money Flower.
Jang Hyuk also had a brief career as a rapper. He released his rap album titled TJ Project in 2000 under the stage name TJ. In August 2013, he published the book Jang Hyuk, Hot-Blooded Man featuring a collection of personal essays.
In 2004, Jang Hyuk and his fellow actors Song Seung-heon and Han Jae-seok were found to have illegally avoided their mandatory military service. Jang Hyuk apologized over the issue and then proceeded to serve his two-year term. Jang Hyuk has been married to his wife Kim Yeo-jin since 2008. They have two sons and a daughter together.