To begin with, his reign was spent fighting off Viking raiders, but in 904, at the Battle of Scones, he achieved a decisive victory and the Vikings were driven from the Scottish mainland. Thereafter his main concern was his southern border, with Saxon Northumbria, where the Vikings had resettled themselves, under Ragnall. Eventually, by 918, he had fought them to a standstill, and obtained the peace he needed.
In 943, after an impressive reign, he abdicated in favour of his cousin Malcolm I, and retired to the monastery of St.Andrews, where he later became Abbot and died, in 952. His surviving son Indulf succeeded Malcolm on the throne.