He was a son of Muryeong of Baekje and is best known for making Buddhism the state religion, moving the national capital to Sabi (present-day Buyeo County), and reclaiming the center of the Korean Peninsula.

Seong was known as a great patron of Buddhism in Korea, and built many temples and welcomed priests bringing Buddhist texts directly from India.

[1] He completely reorganized the administration of the country to strengthen central control, to counteract the political power of the noble clans.

With the aid of Silla and the Gaya confederacy, Seong led a long campaign to regain the Han River valley, the former heartland of Baekje which had been lost to Goguryeo in 475.

However, under a secret agreement with Goguryeo, Silla troops, arriving on the pretense of offering assistance, attacked the exhausted Baekje army and took possession of the entire Han River valley.

The American scholar of Asian cultures Ernest Fenollosa describes the Guze Kannon he uncovered at Hōryū-ji along with the Tamamushi Shrine as "two great monuments of sixth-century Corean Art".

[5] It is referred to by the authors of The Cambridge History of Japan as one of the "great works of Asuka art created by foreign priests and preserved as Japanese national treasures".