In 673, the same year Clotaire died, Ansbert renounced his secular pursuits and became a monk of the Benedictine order. Six years later, he was elevated to abbot of his monastery, the illustrious Fontenelle Abbey. He followed two other saints in that office: Wandrille, the abbey's founder and first abbot, and Lambert, the second abbot, who vacated the office when he was named bishop of Lyons. Under his leadership, Fontenelle prospered. His enterprises included a great expansion and refinement of the abbey's library, and the establishment of local hospitals for the poor.