Interior
The interior has rock-faced walls and Bath stone dressings. The nave has a 3-bay S arcade with double-chamfered 2-centred arches on round piers and responds. The roof, of 3 main bays with a ½ bay at the W end, has arched-brace trusses on corbels, and windbraces. The 2-centre chancel arch is on corbelled capitals. In the chancel are segmental pointed arches to S chapel and N organ chamber, both double-chamfered and dying into the imposts. The E end is elaborately treated. The rere arch to the E window has ringed shafts and a sill band with foliage frieze directly below the window. A mosaic reredos, dated 1876, depicts the Crucifixion and is flanked by decorative-tile panels. The chancel floor is also laid with decorative tiles. In the S wall are double sedilia with pointed arches and on the N side is a cusped aumbry. The S chapel is entered through a segmental-pointed arch from the S aisle and has a doorway with shouldered head to the vestry.
The octagonal freestone font has quatrefoils around the bowl, with inset motifs in marble including the Star of David and IHS monogram. Its stem has attached shafts with broad foliage capitals, and an octagonal base. Pews and pulpit are simple, and the communion rails have iron uprights with scrolled brackets to a moulded wooden rail. A wall monument by Daniel Mainwaring of Carmarthen, salvaged from the previous church and re-set above the N door when the new church was built, commemorates the Rev Edward Picton (d 1835). In a classical style, it has fluted pilasters and entablature, surmounted by a closed urn.
Several windows have stained glass. Chancel windows are all of c1882. The E window, depicts scenes from the Life of Christ including the crucifixion and ascension, by Burlison & Grylls. The S window, by the same firm, shows St Mary. The N window depicts St Thomas, and commemorates the architect of the church. In the nave, the window on the E side of the N wall shows New Testament scenes, c1884. To its L is a window by AL Moore of London, commemorating Glanmor Williams, killed in the Boer War in 1900. It depicts the 'Good and Faithful Servant' flanked by SS George and David. In the S aisle, the central window, by Janet Hardy and dated 1991, is a depiction of the church. To its L is a millennium window installed 2002 and showing Virgin and Child. In the S chapel is an undated window by Celtic Studios of Swansea, showing Virgin and Child, flanked by figures of SS David and Ishmael.