Carreg Cennen Castle occupies a limestone crag above the River Cennen, a naturally defensible position used long before the present masonry was built. The district lay within the Welsh kingdom of Deheubarth, and medieval tradition and documentary evidence associate an earlier stronghold here with its princes. Control of the castle changed repeatedly as native Welsh rulers competed among themselves and resisted English expansion. Its commanding position above routes through the western Black Mountain made it valuable not simply as a refuge, but as a statement of authority over a contested border landscape.

During the thirteenth century, Carreg Cennen figured in the struggles among the descendants of the Lord Rhys and in the wider conflict between the princes of Wales and the English Crown. Rhys Fychan recovered it in the 1240s, but alliances and military pressure continued to shift. After Edward I conquered independent Wales in 1282–83, the castle entered the orbit of the new royal administration. Edward granted the lordship to John Giffard, whose family is generally credited with rebuilding most of the surviving fortress in stone.

The new castle exploited the cliff as part of its defense. A compact inner ward contained domestic ranges and towers behind a powerful gatehouse, while an outer ward provided additional space and protection. Builders cut a passage down into the rock to a natural cave, sometimes described as a dungeon but more plausibly used in connection with water, storage, or emergency access. These features combined military caution with the requirements of a noble household. Later lords maintained the stronghold as one element in a network of estates rather than as an isolated mountain fortress.

Carreg Cennen returned to active conflict during the revolt of Owain Glyndŵr in the early fifteenth century, when royal officers sought to secure castles across Wales. In the Wars of the Roses, it was held for the Lancastrian cause. Yorkist forces captured it in 1462 after a campaign against remaining Lancastrian positions. Because its strength could shelter future resistance, the victors ordered the castle slighted. A large workforce dismantled roofs and damaged walls, ending its effective military life, although the dramatic core proved too substantial and inaccessible to erase.

The ruin later formed part of a working farm and became celebrated by artists, antiquarians, and travelers for its spectacular setting. Unlike many castles absorbed into urban growth, Carreg Cennen remained closely tied to the agricultural landscape around it. Conservation has focused on stabilizing the exposed masonry while preserving the character of the ruin. The site now illustrates several phases of Welsh history at once: princely competition before the conquest, the imposition of Anglo-Norman lordship, adaptation to elite domestic life, and deliberate destruction during a dynastic civil war.