St Peter's Church is situated at the junction of Proiry Street, St Peter's Street and Church Street. The church is located on the site of a Roman defensive gateway. The church was a parish church during the medieval period, belonging to the Deanery of Carmarthen. Between 1107 and 1124 King Henry I granted the church to Battle Abbey, Sussex. It was transferred to the Priory of St John, Carmarthen. A chantry chapel is known to have been established here by 1394. At the dissolution, St Peter's, along with its dependent chapels at Llangain, Llanllwch and Newchurch, fell to the Crown. The church remained in the patronage of the crown until 1816, when it was ceded to the Principal and Tutors of St David's College, Lampeter. By 1907 the church was in the gift of the Bishop of St Davids. The church has hosted the Consistory Courts of the Chancellor of the Diocese of St Davids since at least the sixteenth century. Robert Ferrar, Bishop of the diocese of St David's, was tried here in 1555, before being burned at the stake in Carmarthen's market square (now Nott Square). A crudely carved figure, lying loose in the church, may date to the twelfth century. The churchyard has a lych gate, erected as a memeorial to Reverend Latimer M. Jones, (vicar 1863-1877) in its north-west boundary. The lych gate is considered a good piece of later Victorian Gothic work.

The church is a Grade I listed building, constructed of limestone and Old Red Sandstone rubble. It consists of five-bayed nave, three-bayed chancel, north transept (unusually set one bay west of the chancel arch, now the lady chapel), bolierhouse (possibly a former charnel-house, west of the transept),seven-bayed south aisle, south-east porch, south porch, three-storeyed west tower, transeptal clergy vestry (north of chancel central bay), adjoining choir vestry and adjoining WC block (north of chancel east bay). The nave and chancel are thought to date to the fourteenth century. The tower is thought to be late fifteenth century in date. The south aisle is thought to have been added during the sixteenth century (possibly absorbing a former south transept), and the nave and chancel are thought to have been largley rebuilt and heightened to correspond with it. The south porch is thought to also date to this time. The boilerhouse may date to the seventeenth century. An alter table dated 1716 is reportedly lying loose in the south aisle's east bay.

There are three wallpaintings in the church, which are tables of benefactions dated 1731 with fading gilt lettering. The clergy vestry was added in the early eighteenth century (before 1751). In 1753 a gallery had been added at the south end of the church. Oolite ashlar crenellations were added to the tower in 1770. In 1785-1790 new roofs and plaster ceinings with cornice, by John Nash, were added. The church was also reseated and a west gallery added. The church was restored in 1855, when it was entirely refenestrated and the plaster stripped exposing the rood loft stairs. Restoration continued through the 1860s and 1870s. The choir vestry and south-east porch were added in the nineteenth century. The WC block was added in the twentieth century. In 1969 the south porch was converted into a war memorial chapel, and its external doorway was replaced with a pointed window.

Sources include:
Cadw, Listed Buildings Database
Cambria Archaeology, 2000, Carmarthenshire Churches, gazetteer, 48
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021), pp. 70, 73, 75, 79, 230.

RCAHMW 2021