Dagobert arrived with the Pisan fleet that had come to help the Crusaders besiege the towns along the Mediterranean coast in 1100. He had been appointed by Pope Paschal II, and replaced the temporary patriarch, a Norman priest named Arnulf of Chocques. Dagobert wanted the Kingdom of Jerusalem to be a theocracy, with the Pope at its head, and the Patriarch as the Pope's representative. Godfrey of Bouillon, the first king, promised to turn over the crown to the Papacy once the Crusaders conquered Egypt, which would then become a secular kingdom to replace Jerusalem. However, the invasion of Egypt never came, and Godfrey soon died, while Dagobert was with the army besieging Jaffa. Dagobert attempted to claim Jerusalem for himself, but the nobles took advantage of his absence and proclaimed Godfrey's brother Baldwin of Boulogne as the new king. Upon his return, Dagobert reluctantly crowned Baldwin in Bethlehem, as he refused to crown the new king in Jerusalem itself. Baldwin frequently quarrelled with Dagobert, and in 1102 when Dagobert went to Rome to report to the Pope, Baldwin briefly replaced him with a much more compliant Patriarch, a minor priest named Ehremar. However, Ehremar was quickly deposed when Dagobert returned.
Dagobert remained Patriarch until his death in 1107, and was succeeded by Ghibellin of Arles.