William was born in Toulouse, France, around the year 1297. At the age of 19 he entered the Augustinian monastery in his native city and was sent to study in Paris where he received the title of lector in theology. Afterwards he devoted himself especially to the ministry of preaching, for which he became well known and respected, and through which he drew many others to embrace the religious life. Except for a brief period when he was Prior in Pamiers, he seems to have spent his whole religious life in Toulouse, in the monastery of Saint'Etienne, where, in 1341, the Order's General Chapter was held. William died in Toulouse on May 18, 1369 and was buried in the cemetery of his monastery. Not long after, because of the veneration of the people who regarded him as a saint and wonder-worker, his remains were transferred to the chapel of Saint Mary Magdalene where he was accustomed to celebrate Mass. Leo XIII confirmed his cult in 1893.
William's methodology as a preacher was: pray, contemplate, and only then speak of God, otherwise the preacher's words will not touch the heart of his listeners, but become lost in the rafters of the church. As a man of prayer and recollection, he was much sought after as a spiritual director and exorcist.