He tells us of a quest for the truth which led him little by little to recognize God the Creator and the incarnate God who died to give us eternal life. Baptized in about 345, he was elected Bishop of Poitiers around 353-354. In the years that followed, Hilary wrote his first work, Commentary on Saint Matthew’s Gospel. It is the oldest extant commentary in Latin on this Gospel.
In 356, he took part as a Bishop in the Synod of Béziers in the South of France, the “synod of false apostles”, as he himself called it, since the assembly was in the control of philo-Arian Bishops who denied the divinity of Jesus Christ. “These false apostles” asked the Emperor Constantius to have the Bishop of Poitiers sentenced to exile. Thus, in the summer of 356, Hilary was forced to leave Gaul.
On returning to his diocese in 361, Hilary spent most of the first two or three years trying to persuade the local clergy that the homoion confession was merely a cover for traditional Arian subordinationism.
In about 361, with Hilary’s encouragement, Martin, the future bishop of Tours, founded a monastery at Ligugé in his diocese.
In 364, Hilary extended his efforts once more beyond Gaul. He impeached Auxentius, bishop of Milan, a man high in the imperial favour, as heterodox. Emperor Valentinian I accordingly summoned Hilary to Milan to there maintain his charges. However, the supposed heretic gave satisfactory answers to all the questions proposed. Hilary denounced Auxentius as a hypocrite as he himself was ignominiously expelled from Milan. Upon returning home, Hilary in 365, published the Contra Arianos vel Auxentium Mediolanensem liber, describing his unsuccessful efforts against Auxentius.
According to Jerome, Hilary died in Poitiers in 367.
To this day one of the terms of the English courts and the Spring semester of the Universities of Oxford and Durham are called Hillary term, because they traditionally commence on or about January 13, the day of Saint Hilary.