The Lordship of Glamorgan was one of the most powerful and wealthy of the Welsh Marcher Lordships. The seat was Cardiff Castle. It was established by the conquest of Glamorgan from its native Welsh ruler, by the Anglo-Norman nobleman Robert FitzHamon, feudal baron of Gloucester, and his legendary followers the Twelve Knights of Glamorgan. The Anglo-Norman Lord of Glamorgan, like all Marcher lords, ruled his lands directly by his own law: thus he could, amongst other things, declare war, raise taxes, establish courts and markets and build castles as he wished, without reference to the Crown. These privileges were only lost under the Laws in Wales Acts 1535–1542. Though possessing many castles, the main seat of the Lordship was Cardiff Castle.

The Welsh Marches is an imprecisely defined area along the border between England and Wales in the United Kingdom. The precise meaning of the term has varied at different periods.