St Gwynog's Church, St Twynnells, lies within a rectilinear churchyard, in a prominent hilltop location, overlying a ridgeway which may be prehistoric in origin and formed the primary axis of an enclosed, co-axial field system. St Twynnells parish boundary, and the boundary of the adjacent parish of Warren, follow the co-axial field system boundaries. St Twynnells Church and St Mary's Church, Warren (NPRN 300436) are approximately equidistant from Castle Park defended enclosure (NPRN 305419) and it is thought that the two parishes may perpetuate prehistoric land units that related to the Iron Age site. The church is also known as St Gwynog's Church. The dedication to St Deiniols (as depicted on historic Ordnance Survey mapping) is reportedly incorrect. The church was a parish church during the post-Conquest period. It was a possession of the Benedictine Priory of St Nicholas, Monkton until 1260, when it was appropriated to the Canons of St Davids Cathedral.

The church is a Grade 2* listed building, constructed of limestone rubble. It consists of 5-bayed nave, 2-bayed chancel, south transept and skew passage, north porch, vestry north of chancel west bay and coal cellar east of the vestry. The square, scalloped font bowl may date to the 12th century. The building has medieval barrel vaulting in the nave, transept, tower and porch. The nave's central bays may be 13th-century in date. Its east bays, with the chancel, may be 13th- to 14th-century. Documentary evidence refers to decorative wall colouring of 13th century date, now destroyed. They included thirteenth century fictive masonry with painted shafts and capitals, voussoirs, and false ashlar with flowers. The south transept, and possibly the former north transept, may date to the 14th-century. The west tower retains its medieval openings. The tower, and possibly the nave west bay, are thought to date to the 15th-century. The church was restored in 1858. The vestry and coal cellar may have been added in the later 19th century.

Sources include:
Cambria Archaeology, 2000, Historic Churches Project, Pembrokeshire gazetteer
Cambria Archaeology, 2003, Early Medieval Ecclesiastical Sites Project, Pembrokeshire gazetteer
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021), pp. 93.

RCAHMW 2022