He had been since 620 Bishop of Phasis in Colchis when the Byzantine Emperor Heraclius, in the course of his Persian campaign of 626, consulted him about a plan for bringing the Miaphysites of Egypt back to the Church, and to the support, of the empire.
When Caliph Umar the Great's general, 'Amr ibn al-'As known to the Romans as Amru, threatened the Prefecture of Egypt, Cyrus was made prefect and entrusted with the conduct of the war.