After the death of Marcward in 853, Ado went to Rome where he stayed for nearly five years, and then to Ravenna, after which Remy, archbishop of Lyon, gave him the parish of Saint-Romain near Vienne.
The following year he was elected archbishop of Vienne and dedicated in August or September 860, despite opposition from Girard, Count of Paris, and his wife Bertha.
The Royal Library of Copenhagen preserves an unedited martyrology which dates back to the 11th century and comes from the Abbey of Santa Maria, Serrateix, with information on Ado of Vienne, the Rule of Saint Benedict and other abbots and monks of that time.
[6][7][8] Ado's chronicle is based on that of Bede, with which he combines extracts from the ordinary sources, forming the whole into a consecutive narrative founded on the conception of the unity of the Roman Empire, which he traces in the succession of the emperors, Charlemagne and his heirs following immediately after Constantine VI and Irene.
"It is," says Wilhelm Wattenbach, "history from the point of view of authority and preconceived opinion, which exclude any independent judgment of events.