At age 9, he left home and entered the Buddhist priesthood, learning Buddhism at the Muryangsa Temple in Haeyang (currently known as Gwangju), and, at age 14, he was ordained as a monk by the Elder Daeung. Later, he developed discipline by visiting various Buddhist lecture halls and temples, and he was evaluated as the most excellent student of Gusan Saseon Buddhist Schools by his colleagues. At age 22, he applied to enter the Buddhist division examination, and topped the most prestigious examination for priesthood. He then practiced Buddhism at the Bodangam Hermitage in Posan Mountain (Biseulsan Mountain in Hyeonpung). Then, while staying for 22 years at various temples in Posan Mountain, he practiced various Buddhist faiths and philosophies without indulging in particular faiths or sects.

At age 44, in 1249 (the 36th year of King Gojong’s reign), Il-yeon was invited to lead the Jeongnimsa Temple, which was established by Jeong An. At age 54, in 1259 (the 46th year of King Gojong’s reign), Il-yeon became the Prime Priest. Two years later, in 1261 (the 2nd year of King Wonjong’s reign), he was invited by Wangmyeong to engage in Buddhist activities at Seonwolsa Temple in Ganghwa. In 1264 (the 5th year of King Wonjong’s reign), Il-yeon moved to Ooesa Temple in the Unjesan Mountain in Yeongil, and, then, he moved to Inhongsa Temple in Posan Mountain. In 1274, when King Chungryeol was inaugurated, he reconstructed the Inhongsa Temple in Posan Mountain where he had stayed for 11 years, and renamed it as Inheungsa Temple at the king’s order. He also reconstructed Yongcheonsa on the east of Posan Mountain, and renamed it as Builsa Temple, among other activities. The following year, he compiled and published Yeokdaeyeonpyo Chronicle at Inheungsa Temple.

At age 72, at the order of King Chungryeol in 1277 (the 3rd year of the king’s reign), he led Unmunsa Temple and further practiced Buddhism. King Chungryeol, during the 8th year of his reign, then ordered him to lead Gwamgyeonsa Temple in Gaegyeong. At age 78, the following year, he was ordained as the most esteemed state priest by the king, receiving the title, Wongyeongchungjo. He was so named instead of state priest, because the Chinese Yuan interfered in Goryeo’s affairs and ordered not to use the term, state priest. Il-yeon later moved to Ingaksa Temple where he held Gusanmundohoe, the general assembly of nine Buddhist Mountain Schools, twice, in an effort to reorganize the Buddhist Schools under the control of the Gajisanmun Mountain School. In the spring of 1289 (the 15th year of King Chungryeol’s reign), Il-yeon ordered the publication of Incheonbogam Exemplar at Ingaksa Temple before he passed away at age 84 in July that year. He posthumously received the title, Bogak, and the Buddhist title, Jeongjo, from the king.