Park Eun-seok made his acting debut in 2010 with roles in the SBS series Athena: Goddess of War and in the play Cats on the Roof. In 2013, he became part of several stage productions such as True West and Hamlet. He then played supporting roles in the SBS mystery-thriller Village: Secret of Achiara in 2015 and in the MBC romantic comedy One More Happy Ending in 2016. He also continued to perform on stage, appearing in the plays The History Boys in 2016 and The Elephant Song in 2017. In 2018, he joined the main cast of MBC’s Investigation Couple, which earned him an Excellence Award nomination at the MBC Drama Awards. In 2019, he received a Best New Actor nomination at the KBS Drama Awards for his work in Doctor Prisoner. His career breakthrough came in 2020 when he was cast in the megahit SBS series Penthouse, which won him Best Supporting Actor at the SBS Drama Awards. He also appeared in the drama’s second and third seasons, which both aired in 2021.

Park Eun-seok and his family immigrated to New York when he was a child. He volunteered to undergo mandatory military service in South Korea despite being a permanent resident of the United States. He gave up his U.S. permanent residency after his military discharge.