Narberth's earliest mention is in the Mabinogion as the home of Pwyll, Prince of Dyfed, and the place where Rhiannon was imprisoned and forced to tell her story to passers-by and carry travellers through the gates as penance for allegedly killing her son. However, it is not certain that the castle was situated in the location of the later Norman fortress - although that site is the strongest contender. The Norman Narberth Castle was built in 1116AD initially as a motte and bailey enclosure. The stone structure dates from the late 13th Century.

Despite changing hands on a number of occasions, the castle never fell to an attacking force during the medieval period and remained in English hands during the Glyndŵr Rising of 1400–1415AD. It's believed to have been inhabited until the English Civil War, but by then was already falling into a state of disrepair. The castle was finally slighted after being taken by Cromwell's forces sometime around 1648AD.

Narberth Castle remained inaccessible to the public and in an unsafe condition until 2005AD. At that time, Pembrokeshire County Council obtained a 99-year lease and finalised extensive works in conjunction with CADW to make the ruins safe. The castle was then re-opened to the public and made free to access.

Today, the castle remains open, but safety concerns have caused CADW to install metal fencing to limit access to certain areas. This has already been bypassed though, so it's open to question whether the ruins will be closed off again. As of October 2024, access was still possible. The exact safety concerns are unclear.

Narberth Castle is nestled in a magical little spot on the edge of a thriving market town. It's a little tucked away and easy to miss, which adds to the charm. Remains include a rectangular enclosure, two round-towers, the shell of the great hall, and a vaulted cellar.