Interior
Plastered walls, ashlar pointed reveals to openings. Nave has broad scissor-rafter roof. Ashlar W tower arch, double-chamfered pointed arch dying into jambs. Tower has high ceiling, walls stepped in at about 3m height. Nave has later C19 band of mosaic each side above pews, vine trail. Ashlar chancel arch of two orders, the inner one carried on corbelled wall shafts. Fine later C19 chancel detail including low red marble wall and chancel step with very ornate wrought iron and bass screen by Skidmore (see below). Boarded panelled chancel roof with moulded ribs and bosses, 7-sided, with moulded brattiched wallplate. Pointed arch to N organ-chamber dying into jambs. Fine mosaic chancel floor in blue, red, white and yellow with IHS motif in centre. Marble step to sanctuary. Fine mosaic floor with two mosaic round panels each with 5 roundels (Evangelist symbols, pelican and doves). Green marble altar step. E end wall has exceptional alabaster reredos and flanking wall-cladding. Two-bay sides have pointed arches with marble shafts and brattished cornice. Triple gabled reredos has gables on short columns, over cusped pointed sculpture niches. Centre gable has crockets and finial. Three carved alabaster scenes in niches: Entombment, Deposition, and Resurrection. Ashlar triple lancets to E window in splayed pointed reveal with moulded arch dying into jambs. Alabaster cusped pointed recess on N wall with hoodmould and red marble shelves. Organ chamber is lined in red brick banded in black, with scissor-rafter roof.
Fittings: Medieval round stone font, tapered in below to round shaft. Medieval stoup in porch, with incised bands. Oak later C19 nave pews with shaped bench ends and fielded-panelled backs. Two earlier C19 painted boards with 10 Commandments.
Late C19 fittings include fine brass pelican lectern on twisted stem with polished semiprecious stones. Alabaster pulpit with 3 red marble steps up, curved base and curved front with leaf bosses in upper and lower cornices, and niche with carved Good Shepherd. Exceptional wrought-iron and brass chancel screen by Skidmore of Coventry, of three bays each side of centre. Centre is gabled with scrollwork, scrolled crockets, and supports a large, ornate brass cross inset with large semiprecious stones. Scrolled double gates and lower panels to side bays, which have thin shafts and scrolled pointed heads, and scrolled top rail with cresting and finials. Oak chancel stalls with pierced Gothic arcaded fronts, inscribed 'And our mouths shall show forth thy praise', scrolled tops to bench ends and carvings of musical instruments, and band of foiled circles. N stalls have wrought-iron screen by Skidmore behind. Two hanging chancel lamps, and 2 wall lamps. Altar rails with twisted standards and scrolls.
Inscribed stones: On tower E wall, (formerly built into wall of the Watkins mausoleum) an important incised stone (possibly a cross shaft), C10-11, of some 7 to 8 feet (2 to 2.5 metres) with Latin cross with knotted ends, and plaitwork in each corner, over a crude relief figure holding ?club and dagger, with knotwork in surround. Rope-mould panel below with inscription ? '+ BRIAMAIL FLOU' and panel of plaitwork below. (Another stone, inscribed Catuc, was found built face-inwards to tower arch, but had been lost by the 1870s).
Memorials: Eleven incised floor slabs reset against tower walls: C17 and C18, including on N one of 1601, one to Abigail Davies died 1769, by Games, one to William Prytherch died 1776. One on S to Margaret Jones of Loeger, died 1795, painted classical low relief decoration, by Samuel Williams of Builth. Nave N memorial of 1793 to William Prytherch of Llandefaelog House, died 1776, with Adam-style urns, in grey and white marble. Marble plaque to Penoyre Watkins 1721-92 erected 1819 by his son the Rev. Thomas Watkins of Penoyre, commemorating also his two children Pen'aur and Julia, who died young 1812 and 1818.
Stained Glass: E three-light 1857 by Thomas Ward with seven scenes from life of Christ, on blue grounds. Nave has four 2-light windows with patterned quarries of c. 1857. Tower W window has 2-light of angels, in style of Kempe, death-date 1902. Late C19 patterned glass in porch.
Organ: Removed from St Mary's Brecon c. 1890.
Bells: Two C15 from Gloucester, two of 1715 from Brecon, one recast in 1981, and two of 1889.