St Sadwrn's Church is situated within an irregularly shaped, curvilinear churchyard. The village pound (NPRN 32660) is situated within the south-western churchyard boundary. During the medieval period the church was a chapelry belonging to the Deanery of Stradtowy. In 1196 the benefice, along with the neighbouring chapelry of Llanwrda, was confererred upon Talley Abbey (NPRN ) by Rhys ap Gruffudd (the Lord Rhys). In 1539 the church is thought to have been a parish church, although Llanwrda was still a chapel. At the dissolution the posessions of Talley Abbey fell to the Crown. Henry VIII granted the patronage of Llansadwrn vicarage to Sir Rhys ap Gruffudd, and subsequently (after the former was convicted if treason) to Thomas Jones, Kt., Haroldston, Pembrokeshire. The church's south chapel is known as the 'Abermarlais Chapel', after its patrons at the nearby Abermarlais mansion.

The church is a Grade II listed building, constructed of limestone rubble with some conglomerate. It consists of four-bayed nave, two-bayed chancel, south chapel incorporating south transept south porch and west bellcote. The nave and chancel are probably contemporary and may date to the thirteenth century. There is thought to have formerly been a north door. The octagonal limestone font is thought to be fifteenth century in date. The south transept and porch were added in the fourteenth to fifteenth century, and the former north transept (north of the nave's east bays), may be contemporary. The porch roof may be seventeenth century in date. By the eighteenth century the north transept had been removed and many openings had been blocked. The two bells are dated 1730. The south chapel/transept had been blocked by the mid-nineteenth century. The chuch was restored around the mid-nineteenth century, but this was low-impact. The east windows were altered at that time. The church was again restored in 1883-1884, by by John Middleton and Son. The nave arcade was blocked, as was the west door, and the chancel arch was replaced. The nave chancel were reroofed and reseated, and a new alter rail and pulpit fitted. The inerior of the church was replastered. The medieval west window was blocked in the twentieth century. A new ceiling was inserted in the chapel, and it was replastered, its floor was raised and a partition inserted. The porch was given a floor of flagstones, and a new alter table and credence were fittted. The pulpit was also replaced. During the 1980s, two butresses were added to the chapel wall. The nave was replastered and the plaster was stripped from the chancel walls.

Sources include:
Cadw, Listed Buildings Database
Cambria Archaeology, 2000, Carmarthenshire Churches, gazetteer, 48

N Vousden, RCAHMW, 20 May 2013