Yook Sung-jae debuted with the South Korean boy group BtoB in March 2012. The following month, they released their debut extended play Born to Beat. Meanwhile, their first full-length album titled Complete hit the airwaves in June 2015. In 2016, Yook Sung-jae was introduced as part of the group’s sub-unit called BtoB Blue. They have two non-album singles, namely Stand By Me and When It Rains. In March 2020, Yook Sung-jae released his debut solo extended play Yook O’Clock.

Yook Sung-jae made his acting debut in 2013 through Mnet’s first original drama Monstar. His breakthrough came in 2015 when he starred alongside Kim So-hyun and Nam Joo-hyuk in KBS2’s Who Are You—School 2015, which earned him several Best New Actor nominations. In 2016, he acted alongside Moon Geun-young in the SBS mystery-thriller Village: Secret of Achiara, which won him the New Star Award at the SBS Drama Awards. That same year, he became part of the main cast of the hit tvN series The Lonely Shining Goblin, which scored him several recognitions including Best New Actor at the 10th Korea Drama Awards.

Yook Sung-jae graduated from Dongshin University. However, South Korea’s Ministry of Education cancelled his and six other entertainers’ college diplomas after it was determined that they did not have enough class attendance to fulfill the requirements for graduation. Yook Sung-jae enlisted for his mandatory military service in May 2020 and was officially discharged in November 2021.