He assisted the court in secular administration, but by 790 had been named Abbot of St. Riquier in northern France as well as the governor of Ponthieu. Angilbert spent a great deal of money improving the abbey. He was also a frequent ambassador to the papacy. The first time was to Pope Adrian I, when he delivered Charlemagne's views on the iconoclasm controversy. Later he delivered gifts and assurances of support to Pope Leo III.
Despite his religious status, and there being no record of an official wedding, he had a relationship with the daughter of Charlemagne, Bertha, with whom he had two children. There may have been no wedding, and Bertha and Angilbert escaped the charge of adultery by virtue of their relationship to Charlemagne. A biographer in the 12th century claimed that, prior to his death, Angilbert did great penance for the impropriety of his "marriage." This allowed him to be made a saint, despite the questionable actions of his life.
A fragment of an epic poem about court life, which also details the meeting between Charlemagne and Pope Leo III when the pope fled to Paderborn to escape his enemies in Rome, is sometimes ascribed to Angilbert. Angilbert would have been in a position to witness all that the poem discusses, and he apparently possessed the literary gifts that would have enabled him to produce the poem. Authorship cannot be proven, however.
He died a few weeks after Charlemagne. Louis the Pious, Charlemagne's son and successor, mindful of the potential for family members to challenge his rule, exiled his sisters to various convents. One of Bertha and Angilbert's sons, however, remained active as a Cariolingian historian.