Erispoe was born to Nominoe's wife Argentaela, but the date of his birth is not known. He was involved in his father's campaigns to take control of the Frankish counties of
Rennes and
Nantes. In 843, in alliance with
Lambert II of Nantes, Erispoe took command of the Breton army while his father was ill. Lambert had been displaced as ruler of Nantes by
Charles the Bald, king of
West Francia, who had installed
Renaud d'Herbauges in his place. Ambushed by Count Renaud, Erispoe was badly defeated at the initial engagement at
Messac. However, the Brittons quickly rallied their troops and took the complacent Franks by surprise shortly thereafter at the
Battle of Blain, inflicting a serious defeat resulting in the death of Count Renaud. Having regained his health, Nominoe took command once more. The victory at Blain having secured control of Nantes and Rennes, he raided into Frankish territory, defeating the Franks at the
Battle of Ballon in 845. A truce followed, but after Charles regained control of Nantes, Nominoe and Erispoe renewed their offensive in 849. While on campaign, Nominoe died suddenly. Erispoe was proclaimed leader, but immediately after his father's death, his power was challenged by Charles the Bald, still his nominal
suzerain. Charles crossed the river
Vilaine with an army. Erispoe defeated Charles in the decisive
Battle of Jengland on 22 August 851. ==Treaty of Angers==