St Cennych's Church is medieval in origin, at which time it was a deanery in the Deanery of Kidwelly. It is situated within a polygonal churchyard in the centre of Llangennech.

The pre-1900 church consisted of nave and chancel, north aisle (occupying the length of the nave and the chancel west bay), south transept and west porch. In the sixteenth century the church was noted to have one bell. The 1900 work on the church amounted to a complete rebuilding, apart from the retention of a little of the wall on the north side of the nave. The church's re-worked font is thought to date from the fifteenth century, and there is one early nineteenth century wall monument. Otherwise nothing remains of the earlier parish church.

The current church is a Grade II listed building, considered a well-detailed simple exercise in Gothic Revival, in a church of urban scale which is a prominent feature in the village. It was designed by E M Bruce Vaughan of Cardiff, in the Decorated Style. It was constructed in two phases and completed in 1908. In the first phase of the restoration, in 1900-1901, the old porch and south and west walls of the nave and aisle were removed, and the north wall reduced to a little above ground level. The present nave and aisle were constructed. In 1907-08 the old chancel and vestry were demolished and the present chancel and vestry (including organ chamber) constructed. The tower is also thought to have been added at this time.

Sources include:
Cadw, Listed Buildings Database
Cambria Archaeology, 2000, Carmarthenshire Churches, gazetteer, 48

RCAHMW, 2012.