Though we know that Saint Anthelm was born around 1107 AD in Chambery, Savoy, France, not very much else is known about his early years. At the age of thirty he resigned from an ecclesiastical benefice in the area of the town of Belley so that he could become a Carthusian monk at Portes. Remarkably, after only two years as a monk he was made prior of the motherhouse of his order, the Grande Chartreuse. As prior he was by all accounts a very effective administrator - the community increased, he restored and improved many of the buildings, and standardized the rules. This standardization also allowed for women to be given the opportunity of joining the order in their own homes. One of the more famous monks under him during this time was Saint Hugh of Lincoln.
For twenty four years he served as Abbot until leaving for several years to be a hermit. He returned though, in 1152, to help defend Pope Alexander III against the Antipope Victor IV. After this defense he was made Bishop of Belley by Pope Alexander III (in 1163). He took this role just as seriously as he had as Prior and quickly set out to reform the clergy and regulate the various affairs in his diocese. He famously excommunicated Count Humbert of Maurienne when he took a priest captive and murdered another. When the Pope reversed this excommunication, Saint Anthelm protested saying that he truly did not believe Count Humbert was penitent for his actions and withdrew from his diocese in protest.
Though Pope Alexander commissioned Saint Anthelm to reconcile Henry II and Thomas Becket in England, his health didn't allow for such a journey and so Saint Anthelm continued to care for the poor in Belley. On the morning of June 26th, sick and sensing death was soon approaching, Saint Anthelm called for Count Humbert and recognized that he was in truth sorry for the acts he had committed. He died later that day, June 26th, 1178.
His feast has been celebrated by the Carthusian order since at least 1607 and his feast is still celebrated today on June 26th.