He was heir to the English possessions of his father. By King HENRY I, 1107-77, he was also granted the Lordship of Cardigan.

Gilbert had frequently asked King Henry for land in Wales, indicating that there were rich pickings in Wales even for the most powerful Norman families. Exasperated with fighting with Cadwgan and his kin, Henry determined that one part of their territory should be made safe in the hands of an immigrant lord. In a famous phrase, Henry said to Gilbert "Now I will give you the lands of Cadwgan ap Bleddyn. Go and take possession of it." Gilbert was given an area with one major castle at Cardigan already in use, but with the hinterland little explored. He secured Cardigan and established himself at Aberystwyth (not the later Edwardian stronghold) and commissioned a number of castles, some of which bore or came to bear Welsh names, while others were identified by the name of their French Castellans