Arbeo is thought to have been a scion of the Huosi noble dynasty in the stem duchy of Bavaria.

Arbeo was raised by Corbinians's brother Erembert and prepared for an ecclesiastical career, becoming a member of the Benedictine Order.

At first a priest and notary under Bishop Joseph of Freising and official of the episcopal chancery, he was appointed abbot of the newly founded monastery of Scharnitz in 763.

During his tenure, the Bavarian monasteries of Innichen, Schäftlarn and Schliersee were established, and Scharnitz Abbey relocated to Schlehdorf.

In the long-time quarrels of the Agilolfing duke Tassilo III of Bavaria with his Frankish suzerains, the bishop remained a loyal supporter of King Charlemagne and may have lost his diocese in his later years.