He succeeded his father in 1132 as Prince of Powys. The Chronicle of the Princes of Wales records that "Madog son of Maredudd built the castle of Oswestry" in 1148 and "gave Cyveiliog to his nephews Owain and Meurug, the sons of Gruffudd son of Maredudd".
The Annales Cambriæ record the death in 1161 of "Madoc filius Maredut Powysorum princeps". 1
He was the last of his dynasty to rule as king over the whole of Powys, including, for a time, the Fitzalan lordship of Oswestry. Succeeding his father in 1132, his main pre-occupation, particularly between the years 1149-57, was the defence of Powys against the aggression of Owain Gwynedd. Threatened by the building of the castle of Tomen-y-Rhodwydd at the southern end of the Vale of Clwyd, Madog, in alliance with Ranulf, earl of Chester, unsuccessfully challenged Owain's advance, losing, for a time, the control of his lands in Iâl.
This loss was retrieved in 1157 when Henry II, with Madog's support, made a decisive assertion of authority in North Wales. When he d. three years later he was still friendly with his powerful patron. His praises were sung by the leading poets of the day, and the impression created on the minds of contemporaries by the influence which he asserted in central Wales is enshrined in contemporary prose romances. He was buried in the mother-church of Powys — S. Tysilio at Meifod....
His dominions were divided among a number of minor lords of Powys — his sons and nephews — and were never again to be reunited in the hands of a single ruler. 2