He was tonsured as a monk in ca. 1420, and is considered to have been the confessor of Emperor John VIII Palaiologos. He was a supporter of the Union with the Roman Catholic Church. He played a very active role in the theological discussions. He participated in the preliminary negotiations with Rome at the Council of Basle and later accompanied Patriarch Joseph II to the Council of Ferrara-Florence, where he also represented Philotheus of Alexandria. He was elected Patriarch after the death of the also-unionist Patriarch Metrophanes II.