He was born to Hong Daesun (洪大純), an officer in northwestern Korea. When the Mongols intruded into Goryeo to attack Khitan rebel groups in 1218, Daesun went over to the Mongols. During the first Mongol invasion in 1231, Hong Bok-won greeted the Mongol army and turned against Goryeo. His guidance for the Mongols inflamed Korean animosity against him. He remained in Seogyeong (now P'yongyang) as a Mongol delegate. He was banished and his father was captured by Goryeo in 1234. Ögedei Khan allowed him to settle around Liaoyang and Shenyang and installed Bok-won as an administrator. That was the beginning of Korea] colonies in Liaodong, whose head was later called King of Shen (瀋王). Even though Goryeo released his father, he joined Mongol incursions into Goryeo.
Goryeo sent Wang Jun, a member of the Goryeo royal family, as a hostage to the Mongol Empire. Jun and Bok-won came to conflict with each other. In 1258 he was executed because of defamation by Wang Jun during the reign of Möngke Khan. That brought serious antagonism between Goryeo and his second son Hong Dagu.