Kang Hong-seok made his acting debut in 2011 with the musical Street Life (Run to You). He has since appeared in numerous stage productions such as High School Musical, Kinky Boots, and Death Note. In 2017, he bagged supporting roles in tvN’s Chicago Typewriter and KBS2’s Manhole. In 2018, he joined the hit tvN romantic comedy What’s Wrong With Secretary Kim. In 2019, he was cast in the crime-comedy film Miss & Mrs. Cops. That same year, he played a grim reaper in the top-rating tvN dark fantasy drama Hotel del Luna. In 2020, he acted alongside Lee Min-ho and Kim Go-eun in SBS’s The King: Eternal Monarch. In 2021, he became part of the KBS2 supernatural fantasy series Sell Your Haunted House.
Kang Hong-seok studied theater at the Seoul Institute of the Arts. He married a musical actress named Kim Ye-eun in September 2016. They welcomed their first child in February 2019.