Jang Dong-yoon made his acting debut in the 2016 Naver web series Women at a Game Company. The following year, he started to gain more public attention after starring in the KBS2 teen series School 2017. In 2018, he landed his first silver screen role in the indie film Beautiful Days, which earned him Best New Actor nominations at the 24th Chunsa Film Art Awards and the 56th Grand Bell Awards. Also in 2018, he acted alongside Park Se-wan in the KBS2 series Dance Sports Girls, which won him an Excellence Award at the KBS Drama Awards. In 2019, he was paired with Kim So-hyun in the KBS2 sageuk Tale of Nokdu, which gave him numerous recognitions including an Excellence Award at the KBS Drama Awards. In 2021, he led SBS’ Joseon Exorcist, which was eventually canceled due to supposed historical inaccuracies in its story.
Jang Dong-yoon enlisted for his mandatory military service in May 2012 after his high school graduation. He was discharged in February 2014. In 2015, he received a commendation of appreciation from the Seoul Gwanak Police Station for his bravery that led to the arrest of a convenience store robber. The incident also paved the way for him to enter the entertainment industry.