In 1170 he established the Cistercian monastery of Strata Marcella. He again supported the English in 1173, and was present at the Council of Oxford in 1177. He was the only Welsh prince who refused to support the efforts of archbishop Baldwin and Giraldus Cambrensis in 1188 to preach the Crusade, for which he was excommunicated. It would appear that he handed over the reins of government to his son, Gwenwynwyn (q.v.), in 1195, and retired to the monastery of Strata Marcella, where he d. in 1197, and where he lies buried. His first wife was Gwenllian, daughter of Owain Gwynedd (mother of Gwenwynwyn), and his second wife was a daughter of Rhys ap Gruffydd (q.v.).

In the early years of his reign he excelled as a warrior, and it is as such that Cynddelw (q.v.) sings his praises, but at a later date, Gerald is to speak of him as one of the three princes in Wales who were conspicuous ‘for the justice, wisdom, and moderation of their rule.’ The latter also mentions his eloquent tongue and his sagacity. Yet his fame as a fighter remained, even among the Normans, as can be seen from the ‘Legende de Fulk Fitz Warin.’ It is this aspect of his career that the prince himself reveals in his ‘Drinking-horn of Owain’-a poem patterned on the ‘Gododdin,’ in which a number of fellow-soldiers are each addressed in turn as the horn goes round. It is the best portrayal which we have of the campaigning life of a Welsh prince, with the close comradeship existing between him and his chosen war-band, and the thrill of their life of high adventure. There is also extant (in Myv. Arch., 192 and R.B.H. Poetry, 1395-6) a series of englynion sung by the war-band of Owain to their ‘circuit’ of Wales. The circuit, however, is of North Wales only.