When Charlemagne sent his young son Pepin to Italy as King of the Lombards Angilbert went along as primicerius palatii, a high administrator of the satellite court. Angilbert delivered the document on Iconoclasm from the Frankish Synod of Frankfurt to Pope Adrian I, and served as envoy to the popes on a number of other occasions.
In 790 he was named abbot of Saint-Riquier in northern France (often called by its Roman name, Centula). It was not uncommon for the Merovingian, Carolingian, or later kings to make laymen abbots of monasteries; the layman would often use the income of the monastery as his own and leave the monks a bare minimum for the necessary expenses of the foundation. Angilbert, in contrast, spent a great deal rebuilding Saint-Riquier, and when he completed it Charlemagne spent Easter of the year 800 there.
Angilbert's non-sacramental relationship with Bertha was evidently recognized by the court - if she had not been the daughter of the King historians might refer to her as his concubine. They had at least two sons, one of whom, Nithard, became a notable figure in the mid-9th century. Control of marriage and the meanings of legitimacy were hotly contested in the Middle Ages. Bertha and Angilbert are an example of how resistance to the idea of a sacramental marriage could coincide with holding church offices.