Regino records that "filius suus [=Liutbaldus dux] Arnulfus" succeeded his father as dux in 907. The Salzburg Annals name "Liupoldus dux, pater Arnolfi ducis". His birth date range is estimated based on the likelihood that Arnulf must have been adult and established in his career when he was accepted as his father's successor in 907, but must be considered approximate.
He referred to himself in 908 as ARNULF Duke of Bavaria in a charter confirming an exchange of land between Drakolf Bishop of Freising and Konrad chor-bishop of Freising. "Chuonradus…rex" made donations by charter dated 5 Mar 912 with the consent of "fidelium nostrorum comitum vero Sigihardi, Arnolfi, Erchangarii, Odalrici, Perchtoldi, Chuonradi, Herimanni, Luitfredi atque Iringi", which shows not only that Arnulf was not titled "dux" in official national documents but also that he was considered second in importance among the nobility in the realm at that time, assuming that the order of the names is of significance. He had the power to distribute bishoprics in his territory, although the right passed to the king of Germany on his death. He was expelled from Bavaria by his stepfather Konrad I King of Germany in 915 but soon returned. A reaffirmation of his rule by the Bavarians in 919 is recorded in the 12th century copies of the Salzburg Annals, which imply that he may have been appointed to rule as king in a wider German context, presumably as a rival to Heinrich I King of Germany. He submitted to King Heinrich in 921. "Heinricus…rex" confirmed donations to Kloster Kempten by charter dated 30 Jun 929 at the request of "comitum Arnolfi et Heberhardi". This charter appears to refer to Arnulf and his son, although it is surprising that Arnulf is not referred to with the title "dux".
The necrology of Fulda records the death in 937 of "Arnolt dux". The necrology of St Gall records the death "II Id Jul" of "Arnolfi ducis Baioariorum". 1
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