Irenaeus was likely born in 125 AD in one of the maritime districts of Asia Minor, where Christians predominated and the apostles' memory was still highly revered. St. Polycarp, who had known the apostles or their close followers, had the greatest influence on him.

Numerous Asian priests and missionaries established a local church and preached the gospel to the pagan Gauls. Irenaeus arrived to work as a priest at this Lyon church under the leadership of St. Pothinus, an oriental who was also the church's first bishop. Irenaeus was dispatched to Rome in 177. This mission explains why, during the horrific persecution at Lyons, he was not called upon to partake in the martyrdom of St. Pothinus.

He was going back to Lyons to take up the vacant bishopric. The persecution had ended by then. He became motivated to expose the faults of gnosticism because of its growth throughout Gaul and the havoc it was causing among the Christians in his diocese. He wrote a five-book essay in which he completely lays out the tenets of each group before drawing comparisons between them and the teachings of the Apostles and the Bible. Written in Greek but swiftly translated into Latin, his writings were widely read and effectively killed gnosticism.

Although the exact year of St. Irenaeus's passing is unknown, it is thought to have occurred in 202. The body of St. Irenaeus was interred in a crypt beneath the altar of the church that was formerly known as the church of St. John but was thereafter referred to as St. Irenaeus himself. The Calvinists demolished this grave or shrine in 1562, and it appears that all remnants of him have vanished.

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