He was ordained priest by St. Cyril, but opposed Dioscorus, his successor, on his patronizing Eutyches, and giving into his errors, notwithstanding his endeavor to gain him to his interest, by making him archpriest, and entrusting him with the care of his church. Dioscorus being condemned and deposed by the council of Chalcedon, Proterius was elected in his room, and was accordingly ordained and installed in 552. The people of Alexandria, famed for riots and tumults, then divided; some demanding the return of Dioscorus, others supporting Proterius. The factious party was headed by two vicious ecclesiastics, Timothy, surnamed Elurus, and Peter Mongus, whom the saint had canonically excommunicated. And so great and frequent were the tumults and seditions they raised against him, that during the whole course of his pontificate he was never out of danger of falling a sacrifice to the schismatical party, regardless both of the imperial orders and decisions of the council of Chalcedon.