Gu Ja-sung made his first big screen appearance with a cameo in the 2007 film Milky Way Liberation Front. In 2018, he officially debuted as an actor with a supporting role in the hit JTBC series Misty, which was nominated for Best Drama at the 54th Baeksang Arts Awards. In 2019, he became part of the main cast of the SBS romantic comedy The Secret Life of My Secretary. In 2020, he acted alongside Song Ji-hyo in JTBC’s Was It Love.

Gu Ja-sung attended Dankook University.