He was mentioned by Albert at the Siege of Nicaea in 1097 and at the Siege of Antioch in 1098. William of Tyre says that when Fatimid envoys arrived from Egypt to meet the crusaders, Warner helped escort them back to the coast on their way home. However, Warner and the other escorts were ambushed by the inhabitants of the territory around Antioch when they were returning to the crusader camp. After the crusaders captured Antioch, they were in turn besieged by Kerbogha of Mosul, and Warner was part of the fifth division of the army that marched out to attack Kerbogha.