Sung Joon debuted as a model before turning to acting in 2011 with the KBS2 psychological thriller White Christmas. In 2012, he took on the main male lead role in tvN’s Shut Up: Flower Boy Band. That same year, he won an Excellent Award at the KBS Drama Awards for an episode of the KBS Drama Special called Wetlands Ecology Report. He was then nominated for Best Actor at the 16th Seoul International Youth Film Festival for MBC’s fusion sageuk Gu Family Book and the tvN rom-com I Need Romance 3. In 2014, he acted alongside Jung Yumi and Eric in the KBS2 series Discovery of Romance, which earned him an Excellence Award nomination at the KBS Drama Awards. In 2015, he starred in the SBS dramas Hyde, Jekyll, Me and High Society, which scored him another Excellence Award nomination at the SBS Drama Awards.
Sung Joon enlisted for his mandatory military service in December 2018. In September 2020, he married his non-celebrity partner. They have a child together.