St. William was born in the year 1085 A.D. in Vercelli, Italy, of noble parents. He was orphaned while an infant and was raised by relatives. At 14 years old, he made a pilgrimage to Compostela, in Galicia Spain, a pilgrimage he made barefoot. He was at Mefi in 1106 and spent two years as a hermit on Monte Solicoli. After abandoning a pilgrimage to Jerusalem when he was attacked by robbers, he decided to become a hermit on Monte Virgiliano (Vergine).

One source notes that, shortly after his decision, he healed a blind man, a miracle that brought him instant notoriety. Because of his humility, he did not want to accept the people's praise and admiration so he decided that he would he would live as a hermit on this high mountain. Even there, however, people gathered around him and so he decided to organize them into a community and build a monastery dedicated to the Blessed Virgin. People gave the mountain a new name - Monte Vergine - or mount of the Virgin. It was in the year 1119 that the group became know as the Hermits of Monte Vergine.

Objections soon arose against the strictness of his rule. It is unclear if the objections were internal or external to his community but he and his good friend, St. John of Matera, founded another community on Monte Laceno in Apulia. The hermitages were destroyed by fire so they moved to Monte Cognato in Basilicata. Some time later, he founded monasteries at Conza, Guglietto and Salerno opposite the palace of King Roger I of Naples.

While at this location, St. William became advisor to King Roger. Some were upset by his good standing with the king so they tried to create an negative image of him as an evil man hiding behind a holy habit. They sent a woman to tempt him to sin but as soon as he realized what kind of woman she was he supposedly worked a miracle and the woman ran away frightened.

While some of these stories may well be legendary, it can be confirmed that he founded several monasteries in Italy, the most famous being the first on Mount Virgiliano. The mountain was later named Monte Vergine after his monastery of cenobites that he established under the rule of St. Benedict.

St. William died at the monastery in Guglietto on June 25, 1142.   His feast day is on 25 June.