The cause at Pentretygwyn was established after a section of the congregation at Cefarthen (NPRN 6472) split away due to disagreement over the minister's Arminian leanings. This occurred 1740, and the new cause initially worshipped at a place called Glynpentan, registered for preaching on Jult 10th 1740. The first communions were celebreted by Edmund Jones, Pontypool on August 10th of the same year when 4 were confirmed in person and one accepted by letter. 36 in total took the first communion, and theer appears to have been a steading growth. In 1749 the Williams family donated land at Pantycelyn for the construction of the first chapel.

Pentretygwyn Chapel was built and opened in 1749/1750 and was subsequently rebuilt in 1840. The present chapel, dated 1840, is built in the Simple Round-Headed style of the long wall entry type with a half-hipped roof. The facade is dominated by two tall pulpit windows to the centre, with round-arch heads and florentine tracery to the tops and coloured glass to the morginal glazing. The gallery windows in the outer bays are of similar style, though smaller and simpler in form. There are two dors, both set to the outer bays, which are set with later 19th century panelled doors and with plain overlights. To the centre of the facade is a memorial stone to Edward Jones, while above is a small date/name plaque. The westerly end elevation is slate-hung.

RCAHMW, October 2015