The Barons de Braose

He was also Prince of Wales and was sometimes styled Dafydd I of Wales and Dafydd II of Gwynedd.

In his last years Llywelyn went to great lengths to have Dafydd accepted as his sole heir. By Welsh law Dafydd's older half brother, Gruffydd, had a claim to consideration as Llywelyn's successor. Llywelyn had Dafydd recognised as his named heir by his uncle King Henry III of England in 1220, and also had Dafydd's mother Joan declared legitimate by the Pope to strengthen Dafydd's position.

There was considerable support for Gruffydd in Gwynedd, but although Dafydd lost one of his most important supporters when his mother died in 1237 he had the support of Ednyfed Fychan, the sensechal of Gwynedd. Llywelyn suffered a paralytic stroke in 1237, and Dafydd took an increasing role in government. Dafydd ruled Gwynedd following his father's death in 1240. Although Henry III had accepted his claim to rule Gwynedd, he was not disposed to allow him to retain his father's conquests outside Gwynedd. In 1241the king invaded Gwynedd, and Dafydd was forced to submit. He had to give up all his lands outside Gwynedd, and also to hand over to the king his half brother Gruffydd whom he had been keeping a prisoner. Henry thereby gained what could have been a useful weapon against Dafydd, with the possibility of setting Gruffydd up as a rival to Dafydd in Gwynedd, but Gruffydd died trying to escape from the Tower of London in early 1244.

This freed Dafydd's hands, and he entered into an alliance with other Welsh princes to attack English possessions in Wales. The revolt had some success, and in 1245 King Henry again invaded Gwynedd and built a new castle at Deganwy. Savage fighting followed, but the campaign was ended by the sudden death of Dafydd in the royal home Garth Celyn, Aber Garth Celyn, in February 1246. He was buried with his father at the abbey of Aberconwy.

Since Dafydd's marriage to Isabella, daughter of William de Braose, Lord of Abergavenny had failed to produce an heir, the two sons of Gruffydd, Llywelyn ap Gruffydd and Owain ap Gruffydd, divided Gwynedd between them and continued the war with King Henry through 1246. In April 1247 Llywelyn and Owain met the King at Woodstock and came to terms with him at the cost of the loss of much territory.