Eusebius was the son of a martyr who died in chains. His widowed mother took Eusebius and his sister, both infants, to Rome, where Eusebius was reared, educated, and eventually ordained a lector. He served in Vercelli in the Piedmont, with such success that he was elected in 340 by the clergy and people to govern it. He is the first bishop of Vercelli who is known by name. Eusebius decided that the best way to foster the life of prayer was to live with some of his fellow-clergy as a community of monks. He was the first in the West to combine the monastic discipline with the clerical, an example that was later followed by Saint Augustine.

In 354, Pope Liberius deputed Eusebius and Bishop Lucifer of Cagliari to plead with Emperor Constantius to assemble a council to settle the differences between the Catholics and Arians. They were successful, and the council met in Milan in 355. Although the Catholic prelates outnumbered the Arians, Eusebius realized that the Arians would dominate by force, and he refused to attend until Constantius himself coerced him to do so.

Eusebius's sufferings began with his refusal to condemn the great theologian and doctor of the Church,Saint Athanasius. When the bishops were called upon to sign a condemnation of Athanasius, one of the few bishops who continued to insist that Jesus was both God and man, Eusebius resisted. Instead he presented the Nicene Creed, which he helped to write, and insisted that it be signed by all before the case of Saint Athanasius was considered. This sparked a great tumult.

The emperor sent for Eusebius, Saint Dionysius of Milan, and Lucifer of Cagliari, and demanded that they condemn Athanasius. They supported his innocence, saying he could not be condemned without being heard. They also pleaded that the emperor not use secular force to coerce ecclesiastical decisions. The emperor threatened to execute them but eventually banished them instead.

Eusebius's six years in exile began in Scythopolis in Palestine, where he was put in the charge of the Arian bishop, Patrophilus. He stayed first with Saint Joseph of Palestine, who offered the only orthodox home in the town, and was visited by Saint Epiphanius and others, and given money for subsistence by deputies of his church in Vercelli.

After Count Joseph's death, the Arians dragged Eusebius through the streets half-clothed and locked him in a small room, where they badgered him for four days to conform. Eusebius went on a hunger strike, and after fasting for four days, the Arians returned him to his lodgings. Three weeks later he was molested again; they confiscated his possessions, drove away his attendants, and dragged him away. Later he was banished to Cappadocia, and later still into the Upper Thebaid in Egypt.

Upon the death of Constantius in 361, Julian the Apostate recalled the banished prelates, and Eusebius travelled to Alexandria to plan with Saint Athanasius how to correct the evils of the Church. He took part in a council there in 362, which deputed him to travel to Antioch to effect the council's wish that Saint Meletiusshould be recognized as bishop there, although he had been elected primarily by Arians. It was hoped that this would heal the Eustathian schism. Unfortunately, he found that Lucifer of Caligliari, who had also participated in the council, had widened it by consecrating Paulinus, leader of the Eustathians, bishop of Carthage. This was the beginning of the Luciferian schism.

Unsuccessful, Eusebius travelled over the East and through Illyricum, bolstering the wavering faith of many and bringing others back into the fold. He returned to Italy in 363 and began working in concert with Saint Hilary of Poitiers to oppose the Arianizing Auxentius of Milan.

According to Saint Jerome, Vercelli "laid aside her garments of mourning" upon Eusebius's long-awaited return, but nothing is known of his remaining years. Sometimes he is called a martyr, but this is attributed to his sufferings and not to a violent death.

In Vercelli is treasured a very ancient manuscript of the Latin Gospels that Eusebius is reputed to have copied, the Codex Vercellensis, which is the oldest such manuscript in existence. This and his extant letters demonstrate that Eusebius was a serious scholar as well as a zealous opponent of Arianism. Though it is not absolutely certain, it is believed that he is the author of the Athanasian Creed (Attwater, Benedictines, Bentley, Delaney, Farmer, Walsh, White).