Llanddewi Brefi is the site of the eponymous synod – dated by some as in 545 – where, according to the eleventh-century Life of St David, the saint argued against the Pelagian heresy. While he preached, the ground was miraculously raised beneath him, providing him with an elevated preaching-platform from where he could be both seen and heard by the assembled multitude. The miraculous events at the synod confirmed David’s pre-eminence over his fellow clerics.

The raised location of the church may be because it is sited on a Bronze Age barrow, which seems to also be the case for St Caron’s church not far away at Tregaron. The curvilinear churchyard is bounded on one side by the River Brefi, which might also suggest a pre-Christian religious significance.

Llanddewi Brefi’s continued importance is evidenced by the Celtic clas, a brotherhood of married priests, which flourished here. In 1287, Bishop Beck of St Davids reorganised it as a college of secular canons, which remained until the Reformation. Later, at a time of popular Romanticism, the remote, rural location, with its history of learned Christian devotion, attracted St Davids’ Bishop Burgess and in 1809 he considered founding a new diocesan training college here. However, the gift of land in nearby Lampeter proved decisive in establishing it in that town in 1822, where it remains as a constituent part of the University of Wales Trinity St David.

The imposing crossing tower is probably fourteenth century, with the rest of the building of uncertain medieval date, but much altered, with some demolition, in the eighteenth and nineteenth centuries. R.J. Withers, architect of St Peter’s, Lampeter and associated with works in several other Teifi valley churches, was responsible for stabilising restorations in both 1873–4 and 1885–6, leaving the church much as it is seen today.