Peter reputedly visited the Holy Land about 1093. When Pope Urban II proclaimed the Crusade at the Council of Clermont (Clermont, Council of) in November 1095, Peter began his preaching, traveling from Berry (in central France) across Champagne and down the Meuse valley to Cologne and thence (May 1096) leading his enthusiastic followers across Europe to Constantinople. On August 6 the Crusaders advanced to Nicomedia (modern Izmir, Turkey). Unable to maintain discipline, Peter soon returned to Constantinople to seek help from the Byzantine emperor, Alexius I (Alexius I Comnenus). In his absence, most of his army was annihilated (October 21) by the Turks. He waited in Constantinople until the princely expeditions from western Europe were finally assembled there (May 1097) and accompanied them southeastward across Anatolia. In Antioch he became discouraged by the hardships attending the Crusaders' siege in October and deserted the enterprise (January 1098). He was captured and returned to the Crusade, where he begged forgiveness for his loss of faith.

At last having reached Jerusalem, Peter was appointed almoner of the Christian army in spring 1099. He preached a sermon on the Mount of Olives shortly before the storming of Jerusalem in July, and he conducted processions there in August. He returned to Europe in 1100, becoming prior of the Augustinian monastery of Neufmoustier, which he founded.