The castle dates from a decision in the very early years of the 12th century to entrust Roger, bishop of Salisbury, as lord of Kidwelly.

The Prince of Wales named Lord Rhys, as he was later known, captured Kidwelly Castle in 1159 and was recognised by King Henry II of England as the ruler of the region.

[4] Later in its history, it was unsuccessfully besieged by forces of Owain Glyndŵr in August 1403 with assistance from soldiers from France and Brittany who captured Kidwelly town.

[5] The plan of the castle consists of a square inner bailey defended by four round towers, which overlook a semi-circular outer curtain wall on the landward side, with the massive gatehouse next to the river.

The defensive precautions taken at Kidwelly were not as thorough as those found in the other great Welsh castles of the time, and most of the focus of the builders was in the strength of their walls and towers.