John was a member of the Kamateros family to which belonged the Empress Euphrosyne Doukaina Kamatera, wife of Alexios III Angelos (r. 1195–1203).
An educated man, well versed in classical literature, rhetoric and philosophy, he occupied a series of ecclesiastical posts reaching the post of chartophylax, which he held at the time of his elevation to the patriarchal throne.
[1] In 1198–1200, he had an exchange of letters with Pope Innocent III on the issue of papal supremacy and the Filioque clause.
[2] He intervened in the riots in Constantinople against the arrest of the banker Kalomodios and secured his release,[3] but during the coup of John Komnenos the Fat on 31 July 1200, he hid in a cupboard as the rebels seized control of the Hagia Sophia.
After the capture of Constantinople during the Fourth Crusade in 1204, he initially fled to Didymoteichon in Thrace.