His reign ended when Goguryeo fell to the allied forces of the southern Korean kingdom of Silla and the Chinese Tang dynasty.
For most of his reign, Bojang was a puppet, giving a veneer of legitimacy to Yeon Gaesomun's military rule.
For example, at Yeon's instigation he supported Taoism and issued edicts repressing Buddhism in the country, which had formerly been officially Buddhist.
Yeon Gaesomun defeated major invasions of Pyongyang in 661 and Sasu River in 662, but Silla and Tang were now free to focus and intensify their attacks against Goguryeo.
The Goguryeo capital fell to Silla-Tang forces in the ninth lunar month of 668, and King Bojang was captured.
In 677, the Tang insisted on crowning Bojang as the "King of Joseon" and put him in charge of the Liaodong Commandery (요동주도독 조선왕; 遼東州都督朝鮮王) of the Protectorate General to Pacify the East.