Career before the episcopate
Peter was a native of Alexandria and is described as a highly educated man. He rose through the ecclesiastical ranks of the city, serving as reader, deacon, and priest, and became head of the school of Alexandria, the catechetical school for which the city was renowned. From this teaching office he was elevated to the episcopate, succeeding Bishop Theonas, who had been his own teacher and spiritual guide.
Leadership through persecution
Peter's tenure coincided with the Diocletianic Persecution, the most sustained imperial assault on the Church, which began in 303 and recurred over the next ten years. Driven into exile, he kept contact with his scattered flock through letters and, on his return, ministered in secret to those imprisoned for the faith, encouraging steadfastness and caring for widows and orphans.
A central pastoral problem of the age was the treatment of the lapsed, Christians who had renounced the faith under threat. Peter is recorded as urging leniency toward them. This question brought him into conflict with Meletius, bishop of Lycopolis, with whom he was at one point imprisoned; their disagreement over the conditions for readmitting the lapsed gave rise to the lasting division known as the Meletian schism.
Opposition to Arius
During the same period of unrest, the teaching later associated with Arius, who denied the full divinity of Jesus Christ, began to spread. When Arius refused correction and would not submit to the Church's teaching, Peter anathematized him and excommunicated him from the Church. Tradition holds that even when Arius sent intermediaries professing repentance, Peter discerned the deception and instructed his people not to receive him.
Martyrdom and legacy
Under the emperor Maximian, Peter was arrested and condemned. Asking that his execution be carried out quietly to avoid riots, he was led beyond the walls of Alexandria and beheaded in the year 311, at the spot traditionally identified with the martyrdom of Saint Mark. A pious tradition records that a virgin heard a voice declaring, 'Peter was first among the Apostles; Peter is the last of the Alexandrian Martyrs.'
Peter was esteemed as a theologian, and his writings were later cited at the Councils of Ephesus and Chalcedon. Because he died before the Council of Chalcedon, he is honored as a saint across the Eastern Orthodox, Coptic Orthodox, and Catholic traditions, where he is also remembered under the title 'the Seal of the Martyrs.' His feast is kept on November 25.