St Mallteg's Church was a parish church during the medieval period. It was mentioned in documents of 1398. In 1833 the living was a discharged rectory, in the patronage of the bishop of St Davids. In 1844 the parish of Llanfallteg was described as containing two divisions. The first, comprising 1280 acres, was situated in the hundred of Derllys, Carmarthenshire. The second, comprising 398 acres, was situated in the hundred of Dungleddy, Pembrokeshire. The parish church was St Mallteg's Church. Historic (1890) Ordnance Survey mapping depicts the church in Llanfallteg West (as does modern mapping), with Llanfallteg itself some 1km further to the north-east. Llanfallteg West was situated in the pre-1974 county of Pembrokeshire. After the 1974 local authority reorganisation, the county boundary was straightened, and the parish is now entirely in Carmarthenshire. St Mallteg's Church is sited within a curvilinear churchyard, bounded on its north and eastern sides by buildings and their curtilages, including Llanfallteg Farm and Llanfallteg House (NPRN 96301) (depicted as Upper Llanfallteg Farm on historic Ordnance Survey mapping). In 1998 the church was a parish church, belonging to the Rural Deanery of St Clears. It was redundant, and the churchyard was noted to be overgrown.

The church is constructed of limestone rubble and consists of three-bayed nave, two-bayed chancel, north transept and south porch. The nave is thought to be thirteenth century in date, and is the same width as the chancel. There are large quoins in its west wall. The chancel may date to the earlier fourteenth century. The barrel-vaulted north transept may date to the fourteenth century. A memorial slab dated 1772 is set into the external face of the nave's north wall, and is thought to refer to a phase of repairs. The church was restored in the early nineteenth century, and it is thought that the porch was built at this time, when its floor was flagged with limestone. The church was again restored in the late nineteenth century, and the north transept may have been partially rebuilt at this time. The upper courses of the nave's south wall and porch side walls were rebuilt. The steeply gabled bellcote also dates to this time. The interior was re-roofed, re-floored and re-plastered. The plain limestone font bowl is of indeterminate date. Its base is modern.

Sources include:
Cambria Archaeology, 2000, Carmarthenshire Churches, gazetteer, 48
Lloyd, T, Orbach, J and Scourfield, R, 2006, The Buildings of Wales: Carmarthenshire and Ceredigion

N Vousden, RCAHMW, 13 February 2013