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.
In 1171 the Lord Rhys together with the English king Henry II, who was on his way to Ireland, drove Iorwerth from Caerleon Castle.
After Henry II had traveled on to Pembroke, Iorwerth, his sons and his nephew Morgan ap Seisyll tried in vain to recapture Caerleon Castle.
[1] 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.
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.
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.