St Aidan's Church is situated within a rectilinear churchyard, delineated by a road on its west side and the Cleddau ddu/Eastern Cleddau river on its east side. The site is adjacent to the former Roman road which runs west-east from Carmarthen. Llawhaden was mentioned in a Welsh Law text thought to date to the ninth century as a bishop house. The church is some 140m east of Llawhaden Castle (NPRN 94109), which is thought to be a reused Iron Age enclosure. The church was mentioned as being dedicated to St David in a mid-twelfth-century poem. At this time it was an important prebend of St Davids Cathedral. There is an inscribed stone (NPRN 415026) in the church.

The church is a grade 2 listed building, of medieval date with an unusual double-towered form, retaining significant early fabric and including good interior details. Constructed of lime rubble, it consists of 3-Byed nave, 3-bayed chancel, 2-bayed vestry (formerly a south chapel), south transept with skew-passage and 2-storeyed south tower above (absorbing part of an earlier 3-storeyed tower) and west porch. The nave is thought to date to the twelfth century. The chancel may be fourteenth century and is pierced by a sixteenth century window. The south transept and skew passage are also thought to be fourteenth century. The vestry (former south chapel) is thought to be seventeenth century in date. The arcade separating it from the chancel is of two arches with a round column and moulded caps to the column and responds. The column cap is of conical cushion form with a cable moulding similar to that on the font. The east respond has grotesque carvings, including a two-headed animal in which the heads share one eye, and another face at the rear. The church was restored in 1834, when it was reroofed, its walls were repaired, and a gallery was added. The church was again restored in 1861-2. The vestry was reroofed, the west porch and west door were largely rebuilt, the chancel arch was rebuilt, and the church was refenestrated, reroofed, refloored and reseated. The gallery was removed and the tower parapet was rebuilt.