His nomination was the result of the right of La Rochelle to establish itself as a commune, granted by Guillaume X, Duke of Aquitaine, and upheld by his daughter Eleanor of Aquitaine. Guillaume was assisted in his responsibilities by 24 municipal magistrates, and 75 notables who had jurisdiction over the inhabitants.
His appointment was a consequence of La Rochelle's right to become an independent municipality, sanctioned by Guillaume X, Duke of Aquitaine, and reinforced by his daughter Eleanor of Aquitaine. Guillaume relied on the assistance of 24 municipal officials and 75 influential individuals who had authority over the residents.