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