Between 1307 and 1323, at the behest of Pope Clement V and Pope John XXII, Gui served as the chief inquisitor of Toulouse, publicly styling himself as 'Friar Bernard Gui, of the Order of Preachers, inquisitor of heretical depravity delegated to the kingdom of France by the apostolic authority'. He also assisted the inquisitors of Carcassone, Geoffrey of Ablis and his successor Beaune, and the bishop of Pamiers, Jacques Fournier (later Pope Benedict XII). Gui's inquisitorial work took place in the Languedoc, a region that remained a "stronghold of heresy", in particular Catharism, despite the church's repeated efforts in the area throughout the thirteenth century (such as the Albigensian Crusade of 1209–1229).