The cause dates from 1726 but its origins are earlier and connected to the Puritan, Stephen Hughes (1622–88), known as the "Apostle of Carmarthenshire", who is said to have established a meeting house for Congregationalists in Lammas Street.

The box pews are neatly fitted and there is a most unusual pulpit; this is shaped like a wine-glass with a curved flight of steps.

A similar pulpit is to be found in the nearby Capel Heol Dŵr, which was built in 1831, but they are rare elsewhere having disappeared when alterations and enlargements were made to chapels.

Tabernacle Chapel, Llandovery, built in 1836, has a similar broad interior but differs in having large Gothic windows and a gabled roof.

[4] Capel Heol Awst was designated as a Grade II*-listed building on 19 May 1981, being an example of one of the outstanding early 19th century chapels in Wales, with "strong external architectural character and a good interior".