He was elder son of Prince Gruffydd Maelor and his wife, Angharad, a daughter of King Owain Gwynedd. He succeeded his father jointly with his brother, Owen, in 1191 and on Owen's death in 1197 became the sole ruler of Powys north of the River Rhaeadr and the Afon Tanat.[3]
Madog consolidated the possessions of his father, Prince Gruffudd Maelor, and the territory he ruled became known as Powys Fadog (Fadog in Welsh is a lenited form of his name, Madog) in his honour, the remainder of the old kingdom formed Powys Wenwynwyn. After his death in 1236, this area—comprising Welsh and English Maelor, Ial (Yale), Cynllaith, Nanheudwy and Mochnant Is Rhaeadr—was still referred to as Powys Fadog although it was divided up between his five sons.[3]
Madog was close to his cousin, prince Llywelyn ap Iorwerth, initially, but gradually distanced himself and also kept aloof from 1212 when his cousin had managed to reform the Welsh Confederacy and looked instead to King John of England, in whose pay he was, as an official ally of the English king. By 1215 he decided to ally with his cousin and remained so.[4]