St Martin's Church is is situated within a curvilinear churchyard, whose east and west boundaries are dilineated by streams. A road dilineates the northern boundary, curving slightly to accomodate the churchyard. Some180m west of the church this road terminates as it joins a second road, whose curve may dilineate a former outer enclosure. St Martin's was a chapel of ease during the medieval period, belonging to the Deanery of Carmarthen. It is thought to have possibly been a posession of the Cistercians of Whitland Abbey, but was alienated to the Augustinian priory of St John, Carmarthen, by Walter de Walter de Pederton. At this time the church was referred to as 'the church of Merthier in Derllys (Derllys being the name of the commote), and it subsequently became 'Merthyr Mynach' (the Merthyr of the monks). 1906 Ordnance survey mapping depicts the church as 'St Enfael's', although it is referred to as St Martin's on earlier (1889) and later (modern) Ordnance Survey mapping. In 1998 St Martin's was a parish church belonging to the Rural Deanery of st Clears. an inscribed stone, with Latin inscription, is located in the current church porch. It was reportedly identified during the excavation of foundations for the current church. In 1710 it was reportedly a local tradition (also practiced in Carmarthen) for the graves of people of higher status to be strewn with herbs every Saturday night for a year after the funeral. An arched bier would also be set over the grave every Sunday morning, and would be covered with black (for males) or white (for females).

Nothing is known of the form of the earlier church, except that it seated only 70 people (smaller than the current church) and is thought to have featured a south chapel known as the 'Derllys Chapel'. The octagonal font bowl, thought to possibly date to before the reformation, survives and is located in the current church porch.

The church was rebuilt in 1872-1873 to the designs of R.K. Penson, on the same site and location as its predecessor, but retaining nothing from its earlier fabric. The building is constructed of local snecked rubble stone with yellow oolite dressings. It consists of three-bayed nave and chancel, north transept, north porch and boilerhouse/coalhouse east of the north transept. The openings are neo-gothic single or double lancets.

Sources include:
Cambria Archaeology, 2000, Carmarthenshire Churches, gazetteer, 48
Ordnance Survey, 1889, first edition 25in
Ordnance survey, 1906, second edition 25in
Ordnance Survey, modern, 1:10,000

N Vousden, RCAHMW, 25 January 2013