Irenaeus was born around AD120 in Asia Minor and rose to become Bishop of Lugdunum in AD178. Lugdunum was a large Roman city within the Roman province of Gaul, just south of Lyon in eastern France.
As a boy he heard the sermons by Polycarp of Smyrna who was a disciple of the Apostle John. Irenaeus was impressed by Polycarp's unadulterated teachings of the Gospels and he became a lifelong follower.
He probably accompanied Polycarp on a trip to Rome in AD154 in connection with resolving an argument in the church over the date that Easter should be celebrated. The eastern church celebrated Easter on Nisan 14, the Jewish date of the Passover but the western church celebrated it on the first Sunday following the first full moon following the Spring Equinox. He acted as a mediator between the two opposing sides and appealed for unity to avoid a potential schism in the church over such an unimportant issue.
The Church at this time was experiencing tensions between opposing factions, such as the Gnostics with their alternative teachings, but Irenaeus did not tolerate such teachings and worked hard throughout his life to keep the church centred on the true teachings of the Gospels. Irenaeus was therefore a man of his time and thanks to him we have the faithful teachings of the four Gospels, Mathew, Mark, Luke and John and not a bible containing the disputed Gnostic Gospels. The Gnostics claimed to be Christians, but Christians with a difference. They said that Jesus had had two doctrines, one a doctrine for the common man, and preached to everyone, and the other an advanced teaching, kept secret from the multitudes and only for the chosen few, the spiritually elite.
We do not know for certain how he died but St Jerome stated that he was martyred during the persecution of Emperor Septimus Severus in 202.