Baek Sung-hyun debuted as a child actor in the 1994 film I Wish for What Is Forbidden for Me. He then landed his first TV acting gig in the 1995 KBS2 romance drama Blowing of the Wind. He spent the succeeding years playing the young counterparts of the male protagonists in several TV series such as SBS’s Beautiful Day in 2001 and MBC’s Trio in 2002. In 2003, he appeared in the MBC sageuk Damo and in the SBS romance melodrama Stairway to Heaven. His portrayal of the young version of Kwon Sang-woo’s character in the latter earned him praise from viewers and critics. In 2008, he joined the MBC sitcom Kokkiri, which won him the Hot Sitcom Star trophy at the 2nd Mnet 20’s Choice Awards. In 2010, he acted alongside Hwang Jung-min and Cha Seung-won in director Lee Jun-ik’s action-drama film Blades of Blood. In 2013, he became part of the SBS espionage drama IRIS 2. That same year, he was cast as the male lead in the KBS1 daily series Melody of Love, opposite Dasom. His work in both dramas scored him a Best New Actor nomination at the KBS Drama Awards.

Baek Sung-hyun enlisted for his mandatory military service in January 2018 and was discharged in October 2019. He married his non-celebrity girlfriend in April 2020.