The life of St. Hilary before his appointment as a bishop is not well documented. It is appropriate that the majority of what historians know about him comes from intimate details found in his vast theological writings. According to those comments, Hilary was born into a pagan household in modern-day France, most likely in 310, three years before the Roman Empire formally recognized Christianity to be tolerated.
Hilary himself acquired a thorough education in the Latin and Greek classics but seemed to have little Christian effect growing up. His thorough study of the Bible and Greek philosophy was not out of the ordinary for his time. He realized that the Bible was consistent with philosophy and the sciences, which led him, like many other early Church Fathers, to acknowledge its veracity.
But for him, this was a slow process, and it wasn't until 345—by which point he was married and had a daughter—that Hilary baptized himself and his family to fully embrace the Catholic Church. However, his ascent within the Church was anything but gradual; in 353, the people of Poitiers demanded that he be appointed as their bishop.
By definition, the role required a great deal of personal sacrifice in addition to enormous responsibilities. Even while the early church allowed certain married men to hold the office of bishop, they were customarily expected to maintain celibacy while married, and many of them took up a drastically reduced lifestyle similar to that of monks. After being ordained, Hilary appears to have pursued this austere lifestyle.
Furthermore, Hilary would play a major part in the second wave of the Church's first major theological conflict, which occurred at the same time that he was elected Bishop of Poitiers. Despite the Church's rejection of Arianism, which maintained that Jesus was just human and not divine, being confirmed by the Council of Nicaea in 325, strong forces within the Church and the empire continued to support the heresy.
Just a few years after assuming the position of bishop, Hilary found himself essentially alone in defending Jesus' deity in front of an antagonistic group of bishops in the Gaul region of southern France. The bishops appealed to Emperor Constantius II, who exiled Hilary from Gaul and supported a modified form of Arianism.
By sending Hilary to Phrygia, Constantius II probably had no idea that he would encourage the bishop to present an even stronger defense of orthodox theology. His most significant work, "On the Trinity," which he wrote there, demonstrates how the Bible consistently bears witness to the core mystery of the Christian faith.
Interestingly, this deeply Orthodox bishop was also very benevolent towards people he thought were sincerely incorrect. To support what they understood to be true and guide them into complete commitment to tradition, he worked closely with groups of clerics and faithful whose dogmatic formulations he believed to be only flawed or imprecise, but not purposefully heretical.
During his exile, Hilary even traveled to Constantinople to inform the city's bishops of the emperor's non-orthodoxy. Hilary was allowed to return to his diocese at Poitiers upon Constantius II's passing in 361. He was exiled for fighting Arianism in Gaul, but upon his return, he survived to witness its outright condemnation in the local church.
Late in his life, Hilary took action to promote orthodox teaching in other areas, despite his strong commitment to leading his own diocese. Above all, he condemned the Arian Milanese bishop Auxentius. Later resistance to Auxentius resulted in his replacement by St. Ambrose of Milan, who had a significant impact on St. Augustine's conversion.
After imparting his teachings and manner of life to several followers, for instance, St. Martin of Tours, St. Hilary passed away in Poitiers in 367. In 1851, St. Hilary, who had long been revered and honored as a saint in the Church, was also named a Doctor of the Church.
Other Saints of the Day
St. Andrew of Trier
St. Berno of Cluny
St. Kentigern Mungo
St. Erbin of Dumnonia
St. Leontius of Caesarea