Arnulf gave distinguished service at the Austrasian court under Theudebert II (595-612). In 613, however, with Pippin of Landen he led the aristocratic opposition to Queen Brunhilda of Austrasia that led to her downfall and the reunification of Frankish lands under Clotaire II. About the same year, he became bishop of Metz.
From 623, again with Pippin, now mayor of the Austrasian palace, Arnulf was adviser to Dagobert I, before retiring (629?) to become a hermit. Arnulf's son Ansegisel married Pippin's daughter Begga; the son of this marriage, Pippin II, was Charlemagne's great-grandfather.