He became a Benedictine monk at Monte Cassino, but in 782 received permission to travel to meet Charlemagne to ask for the release of his brother, who had been held hostage by the Franks since participating in a failed revolt of Lombards against the Frankish overlords.
While moving around with the Frankish court Paul wrote a history which records many helpful facts about Charlemagne's ancestors, including Arnulf of Metz, one of the founders of the family. Paul's most important work is his history of the Lombards, Historia gentis Langobardorum. This history, interesting as it is for the record of the 6th, 7th, and 8th century Lombard kings of Italy, is most important as a written record of the semi-mythological figures of earlier Lombardic history.