It is believed that Cyril was born ca. 378 at Theodosiou in Lower Egypt. His maternal uncle, Theophilus, was elected archbishop of Alexandria in 385. It is possible that his uncle supervised his studies in Alexandria as a youth but we do not have any confirmed information about his life until 403. In 403, Cyril accompanied Theophilus to the infamous Synod of Oak at which John Chrysostom was disposed.
After the death of Theophilus and a contested election, Cyril succeeded his uncle as bishop of Alexandria in 412. He continued many of his uncle policies, including unyielding pressure on pagans, heretics and Jews. After 428, he became the leading orator in the conflict with Nestorius, the bishop of Constantinople. In his sermons, Nestorius rejected title of the "Mother of God" (Theotokos) for Mary the mother of Jesus. Against Nestorius, Cyril argued that Jesus was fully divine and therefore one single person and that person was God. For that reason it was accurate to refer to Mary as the Mother of God. Emperor Theodosius II called a council in Ephesus in the spring of 431 to resolve the matter. Before the eastern bishops had arrived, Cyril convened the meeting and subsequently obtained the condemnation of Nestorius. The late arriving Antiochene bishops condemned Cyril and his actions. Theodosius had both Cyril and nestorius disposed and imprisoned. Later Cyril was release and h e negotiated a compromise with Antiochenes. Cyril was rehabilitated but Nestorius was left to his own fate. Unresolved issues continued to be debated even after his death in 444.
Though Cyril is known primarily for his polemical and dogmatic works, Cyril penned a much larger corpus of exegetical works. He produced commentaries on Isaiah, the Minor Prophets, Psalms, Song of Songs, and Proverbs, John, Luke, Matthew and the Pauline Epistles.