Hilary was born to pagan parents of the Gallo-Roman nobility at Poitiers. Educated in the classics, he came to Christ through reading the prologue of John's Gospel, was baptised in adulthood with his wife and daughter, and around 350 was elected bishop of Poitiers by acclamation.
He immediately threw himself into the great trinitarian battle of the 4th century — the Arian crisis — and was exiled to Phrygia in 356 by the Arianising emperor Constantius II for refusing communion with the pro-Arian bishops of Gaul. His four years of exile produced his masterwork, the twelve books of De Trinitate (On the Trinity) — the first major Latin defence of Nicene orthodoxy. Through it he became the principal Western theological link to the Greek fathers.
Returning to Gaul in 360, he rallied the orthodox bishops, deposed his Arian opponents, and won back the West to Nicene faith. Augustine and Jerome quote him with reverence; Pope Pius IX declared him a Doctor of the Church in 1851.