There is considerable doubt about the year of Irenaeus’ birth; estimates vary from 97 to 160. According to tradition, he learned the Christian faith in Ephesus at the feet of Polycarp, who in turn had known John the Evangelist. Some years before 177, probably while Irenaeus was still a teenager, he carried the tradition of Christianity to Lyons in southern France.

The year 177 brought hardship to the mission in Gaul. Persecution brokeout, and theological divisions within the fledgling Christian community threatened to engulf the church. Irenaeus, by now a priest, was sent to Rome to mediate the dispute regarding Montanism, which the Bishop of Rome, Eleutherus, seemed to embrace. While Irenaeus was on this mission, the aged Bishop of Lyons, Pothinus, died in prison during a local persecution. When Irenaeus returned to Lyons, he was elected bishop to succeed Pothinus.

Irenaeus’ enduring fame rests mainly on a large treatise, entitled The Refutation and Overthrow of Gnosis, Falsely So-Called, usually shortened to Against Heresies. In it, Irenaeus describes the major Gnostic systems, thoroughly, clearly, and often with biting humor. It is one of our chief sources of knowledge about Gnosticism. He also makes a case for orthodox Christianity which has become a classic, resting heavily on Scripture and on the continuity between the teaching of the Apostles and the teaching of bishops, generation after generation. Against the Gnostics, who despised the flesh and exalted the spirit, he stressed two doctrines: that of creation being good, and that of the resurrection of the body. He famous wrote that “the glory of God is a human being fully alive, and full human life consists in the vision of God.”

A late and uncertain tradition claims that he suffered martyrdom around the year 202.