St Michael's Church is situated within a curvilinear churchyard (now suboval some 500m north-west of Castlemartin Castle (NPRN 305415). A 7th?9th century cross-incised stone, Castlemartin 1 (NPRN 422363) was discovered in the churchyard wall in 1922 and deposited in the church, but it is now lost. Castlemartin Castle, thought to have been a post-Conquest castle site, may have originated as an Iron Age enclosure and have been reused as an early medieval llys site, with the fields radiating out from it representing an early medieval infield system. If so, church and castle site may have been a pair of kinship enclosures, one of which became an ecclesiastical site. The former Vicarage (NPRN 22507) is situated within the churchyard some 40m north-east of the church. A mounting platform (NPRN 422362) is situated just outside the southern boundary, adjacent to Church Lane. There is also a set of iron rings set in the adjacent wall for tethering horses. The church was mentioned in 13th century documents and listed in the Taxation of 1291. The church was a parish church during the post-Conquest period, belonging to the Deanery of Pembroke. It had at least one dependent chapelry at Flimston. In 1291 the church was granted to the Priory of St Nicholas, Monkton. In 1461 it was transferred to St Albans Abbey, and fell to the Crown at the dissolution.

The church is a Grade I listed building constructed of limestone rubble. It consists of 3-bayed chancel, 4-bayed nave, 4-bayed north aisle with skew-passage, 3-storeyed south transeptal tower and south porch. The 12th century limestone font has a square cushion bowl on a cylindrical stem and base.The nave and chancel are thought to date to the 13th century. The former north and south chapels are thought to have been constructed in the earlier 14th century, with the south and former north transepts constructed in the later 14th century. The lower stage of the tower is thought to have been constructed in the 15th century. The north aisle and porch (formerly two storeys) were constructed in the later 15th century. The belfry stage of the tower was added in the early 16th century. The former west porch was added in the early 17th or early 19th century. The church was restored in 1858, when the vestry was added, which lies over a boilerhouse. The doorways were rebuilt at this time, and the building almost entirely refenestrated. The church was also reroofed, refloored, replastered and reseated.

Sources include:
Dyfed Archaeological Trust, 2000, Historic Churches Project, Pembrokeshire gazetteer
Dyfed Archaeological Trust, 2003, Early Medieval Ecclesiastical Sites Project, Pembrokeshire gazetteer

N Vousden, 17 November 2017