Hugh, of the noble house of Semur, refused a knight's life over his father's objections and entered Cluny under Abbot Odilo at fourteen. He became prior at twenty, was made abbot at twenty-five on Odilo's death in 1049, and held the office for sixty years — the longest reign of any Cluniac abbot.
Under his rule Cluny reached its zenith. The third abbey church, the Maior Ecclesia consecrated in 1095, was for five centuries the largest church in Christendom — surpassed only when the new St. Peter's was completed in the 17th century. The Cluniac network grew to about 10,000 monks in 1,000 dependent houses across the whole of Western Christendom. He served as papal legate, intervened personally in the great drama of Canossa (1077) where he stood as godfather to Henry IV during the emperor's penance before Gregory VII, and was the principal advisor of nine popes from Leo IX to Paschal II.
Six future popes were among his Cluniac monks — including Gregory VII and Urban II — and the entire reform movement of the late 11th century turned on the Cluny–Rome axis that Hugh embodied. He died on Easter Sunday morning 1109 at the great abbey he had rebuilt and was canonized eleven years later by Callixtus II.