He was a son of
Owain ap Caradog and thus a grandson of King
Caradog ap Gruffydd of
Gwent. In 1136 together with his older brother
Morgan ab Owain he attacked and murdered
Richard FitzGilbert de Clare in an ambush between
Abergavenny and
Talgarth. Iorwerth also supported his brother during the subsequent reconquest of Upper Gwent and Llenfennydd. As a result of this close alliance, he became his heir and successor after Morgan's murder in 1158, although Morgan left at least two sons. In contrast to his brother, however, he did not claim the title of king.
Richard de Clare, the Lord of
Chepstow, retook
Usk Castle before 1169. In 1171 the
Lord Rhys together with the English king
Henry II, who was on his way to Ireland, drove Iorwerth from
Caerleon Castle. Iorwerth had to retire to
Machen Castle in Gwynllŵg. After Henry II had traveled on to
Pembroke, Iorwerth, his sons and his nephew Morgan ap Seisyll tried in vain to recapture Caerleon Castle. After the siege failed, they sacked and ravaged the Llefennydd region. In 1172 Iorwerth's eldest son Owain and Iorwerth's brother-in-law
Seisyll ap Dyfnwal, Lord of Upper Gwent, were attacked by soldiers of the
Earl of Gloucester on their way to Usk Castle, where they were going to negotiate with Henry II. While Seisyll was captured, Owain was murdered. To exact revenge, Iorwerth and his son
Hywel plundered large areas of
Herefordshire and
Gloucestershire. When the king's power was weakened by the rebellion of his sons the next year, Iorwerth and Hywel took advantage of this with further attacks and conquests. After a three-day siege, they were able to recapture Caerleon Castle on 21 July 1173, and subsequently also occupy the Lower Gwent. At the beginning of 1175, however, violent clashes broke out within the family. Iorwerth's son Hywel blinded and castrated his uncle Owain Pen-Carn, his father's younger brother. From then on, Iorwerth's nephew Morgan, a son of Morgan ab Owain, supported the English who recaptured Caerleon Castle and Lower Gwent. At the end of June 1175, however, Iorwerth concluded an alliance with Lord Rhys, and under his leadership he was one of the princes of southeastern Wales who paid homage to Henry II in
Gloucester. This gave him back Caerleon. Presumably this was helped by the fact that Iorwerth's daughter
Nest became a lover of Henry II at that time and bore him a son. Nest then married
Ralph Bloet, an Anglo-Norman lord from the neighboring lordship of
Striguil. == Family and issue ==