The cause at Cefnarthen is one of the oldest in Wales, being established by Jenkin Jones of Llanigon as early as 1642 (the date commemorated on one of the two main door heads). After Jones and other members of the congregation were imprisoned in Carmarthen in 1660, they met in a cave on Craigyrwyddon, while the first chapel was built c.1689 after the passing of the 1688 Act of Toleration. In 1740 a part of the congregation split off to form the cause at Pentretygwyn (NPRN 6473), the Cefnarthern congregation moving towards Arminianism, the Pentretygwyn cause towards Calvinism. According to Rees & Thomas (Hanes Eglwysi Annibynnol Cymru) the cause declined after the split and the chapel was at some point used by the Baptists. In 1772 Cefnarthen and Pentretygwyn were reunified, with a meeting on ministers on August 18th of that year, the expenses for which were underwritten by Pentretygwyn.

The chapel was rebuilt in 1853, with minor modifications in 1880 and 1902. The present chapel, dated 1853, is built in the Simple Round-Headed style of the long-wall entry type. The walls are of rubble stone with a roughcast render to the facade, and with a slate roof and cast iron rainwater goods. The facade has two tall, central pulpit windows with round-arch heads and interlacing tracery to the top of the small-paned sash windows, with a further two, smaller gallery windows of identical style to the outer bays. The two doors are aloso set to the outer bays but slightly offset towards the centre from the gallery windows. These are both set with later 19th century panelled doors and plain overlights. In the centre is a small date and name plaque. The stone gable end wall in the east has a small plaque in memory to rev Peter Jenkins, while the west end has a two story lean-to, accommodating a ground floor stable and first floor vestry.

Internally, there is a wine-glass pulpit set against the front wall framed by the pulpit windows. This has a panelled front with concvae sides and four shafts with pendant finials. The panelled pulpit back is pointed, an imitates the intersecting tracery of the windows. In front is a sedd fawr which is enclosed by curved end panelling, from the left end of which run the pulpit steps. There are simple panelled box-pews, set in the usual three blocks but raked to the rear. Another, single, box-pew sits to the right of the pulpit. A gallery is arranged on three side, with the front made of alternating vertical and horizontal panels. The gallery seating is steply raked and made up of open backed benches. The plaster ceiling has a single central ceiling rose.

To the north & north-east of the chapel sits a sizable graveyard.

RCAHMW, June 2016