The Coptic church believes that Peter was given by his parents to patriarch Theonas to be brought up as a priest, as had Samuel in the Old Testament. He rose through the orders, first becoming a reader, then a deacon, then a priest. On his death bed, Theonas advised the church leaders to choose Peter as his successor, which they did. Eusebius states he was patriarch for 13 years (Historia Ecclesiatica VII.32).
The years in which Peter fell during the most terrible persecution Christianity was subjected to, that of Roman Emperor Diocletian, which began in 303, and continued intermittently over the next ten years.
During his imprisonment, he and bishop Meletius of Lycopolis fell into an argument over the treatment of Christians who had either offered a sacrifice or surrendered scriptures to save their lives during the persecution. Peter urged leneincy while Meletius held firmly the lapsed had abandoned their faith and needed to be rebaptised. Their argument became heated, and was ended when Peter hung a curtain between him and Meletius. One of Meletius' followers was Arius.
One of the acts celebrated in Peter's life was that he calmed the populace of Alexandria before his execution, who were at the point of rioting to save his life. He was executed on November 25, 311. Because he is believed to be the last one to lose his life for the faith in the Diocletian Persecutions, he is referred to in church history "The seal of the Martyrs".