In his early youth, or the 420s, Hilary joined the abbey of Lérins which was, at the time, presided over by his kinsman Honoratus. Hilary seems to have been living in Dijon before this, although other authorities believe he came from Belgica, or Provence. Hilary may have been a relative or "even the son" of the Hilarius who had been prefect of Gaul in 396 and of Rome in 408. Hilary succeeded his kinsman Honoratus as bishop of Arles in 429. Following the example of Augustine of Hippo, he is said to have organized his cathedral clergy into a "congregation," devoting a great part of their time to social exercises of asceticism. He held the rank of metropolitan bishop of Vienne and Narbonne, and attempted to exercise the sort of primacy over the church of south Gaul, which seemed implied in the vicariate granted to his predecessorPatroclus of Arles. Hilary deposed the bishop of Besançon, Chelidonus, for ignoring this primacy, and for claiming a metropolitan dignity for Besançon. An appeal was made to Rome, and Pope Leo I used it, in 444, to extinguish the Gallican vicariate headed by Hilary, thus depriving him of his rights to consecrate bishops, call synods, or oversee the church in the province. The pope also secured the edict of Valentinian III, so important in the history of the Gallican church, which freed the Church of Vienne from all dependence on that of Arles. These papal claims were made imperial law, and violation of them were subject to legal penalties. Léon Clugnet suggests that the dispute arose from the fact that the respective rights of the Court of Rome and of the metropolitan were not sufficiently clearly established at that time, and that the right of appeal tothe pope was not explicitly enough recognized. Following his death in 449, Hilary's name was introduced into the Roman martyrology.
Writings
During his lifetime Hilary had a great reputation for learning and eloquence as well as for piety; his extant works compare favourably with any similar literary productions of that period. A poem, De providentia, usually included among the writings of Prosper of Aquitaine, is sometimes attributed to Hilary of Arles.