Double-naved interior with late medieval 4-bay arcade dividing the chambers. This has octagonal piers with chamfered bases and moulded abaci. Both chambers retain their exceptionally-fine late C15 or early C16 roofs, that to the main, S side of eight bays, and that to the N side of nine. The former has hammerbeam principals and arched-braced collar intermediate trusses, with moulded members, pegged construction and fine cusping above the collars; moulded rafters and purlins in compartmented arrangement, with foliated bosses at the intersections. The wall plate has good crenellated brattishing with blind tracery arcading above. The hammerbeam trusses have octagonal shafts with moulded abaci and bases and have carved wooden angel busts. The 2 eastern-most bays form the sanctuary and have a fine waggon roof. This has complex blind tracery panels in 8 tiers with moulded ribs and crenellated brattishing. The wall plates and purlins have vinescroll relief carving, the latter with foliated central bosses, the former with carved angel busts to the centre and ends; each holds a shield bearing instruments of the Passion (the central N side angel is missing).
The N chamber roof is similar for its eastern-most bays, though the angel carvings to the hammerbeams are C17 and of six originally, only three now remain. The four western bays have more conventional arched-braced collar trusses, with 2 tiers of cusped windbraces. Modern parquet flooring to both chambers, with simple early C20 Gothic oak pews with fleurs-de-lis ends; these incorporate several original late medieval bench-ends, from which the remainder have been copied. The N chamber has a medieval octagonal sandstone font with stepped octagonal plinth and chamfered base; plain panelled sides and squat, fluted shaft. At the E end is a pointed arched recess to the N wall, the chamfered arch itself a C19 restoration. Large medieval iron-bound dug-out chest with early C17 poor box post attachment. The chancel (S) has Jacobean-style oak choirstalls, early C20, though made up in part from earlier material; strapwork and gadrooned relief friezes, with carved urn finials. C18 oak altar rails define the sanctuary and return on the N side; fluted columnar balusters. Gothic-style organ at the W end; 1892, by Hope-Jones, inventor of the electric soundboard.
Monuments: S chamber (nave): at the W end, on the S wall is a very fine large baroque monument to Maurice Jones Esq., of Ddol and Llanrhaeadr hall, d.1702; by Robert Wynne, sculptor of Ruthin. The monument is of figured white marble and consists of a life-sized recumbent effigy lying upon a sarcophagus with a dedication inscription to the front. Behind the effigy is a depressed arch with associated carved drapery swags, the latter parted to reveal a black-coloured back panel. Surmounting the arch is a polychromed heraldic cartouche. Encompassing the whole is a fine aedicular Tuscan architectural frame with engaged pilasters and columns supporting a complex entablature. Flanking the effigy and surmounting the columns are life-sized figures of weeping putti. Segmental entablature with central and flanking flaming urns, and garlands in between. To the E of this, on the same wall, are a group of 5 white marble funerary tablets. The first is to Watkin Edwards Wynne of Llwyn, Esq., Major Commandant of the Merionethshire Militia, d.1796. This consists of a high relief sculpture of a mourning muse contained within an oval niche. The whole sits within a plain rectangular architectural frame with moulded base and entablature and flanking pilasters; shaped apron with memorial inscription, and a squat grey marble obelisk above, with applied heraldic roundel. Below this memorial is a simple Grecian-style tablet to Anna Maria Wynne (wife of the above), d.1828. Next are 3 tablets, one above the other: the top one is to David Jones, d.1822, and family, and is by George Owen, sculptor of Hatton Garden, Liverpool; the middle one is to Miles John Thelwall Esq., d.1807, and the bottom one is to the Rev. Robert Roberts of Brynmorwydd, d.1817. To the E of the latter is a simple, tall Gothic-style tablet of sandstone on a black marble background; this is to Henry Meredith Mostyn, RN, of Segryd and Llewesog, d.1840.
Chancel, S wall: A small but fine baroque wall monument to John Lloyd of Brynttyarth Esq., d.1723 (erected 1724). Of light grey figured marble, this consists of a swagged drapery inscription tablet supported by winged putto heads, and with voluted sides. Moulded entablature surmounted by a black painted overthrow with swagged heraldic arms in white marble; shaped apron with winged putto head. Immediately to the W of this monument is a Gothic-style tablet in grey, white and brown marble; to Charles Manford of Llanrhaeadr, d.1890.
N chamber, N wall: To the R of the N door is a small, second-quarter C18 tablet of polished slate to Edward Lloyd; shaped top with relief-carved skull and crossed bones. Below this is a plain black marble tablet to Margaret Roberts, d.1812. Below this is a small brass funerary plaque inscribed to Robert Lloyd of Llwyn, Gent., and his wife Elizabeth, d.1771 and 1766 respectively; shaped top with skull and crossed bones motif. E of these, between the 2 windows are 3 plain classical tablets, one above the other, of white and black marble; to Ambrose Price Esq. (top), d.1813, James Vaughan Horne (centre), d.1848, and finally Major John Griffith Price of Llanrhaeadr hall, who died during the Indian Mutiny in 1858. To the R of the E window of the N chamber (the famous Jesse Window) is a small classical tablet of white and black marble to Elizabeth Roberts of Bachymbyd, d.1841. Below this is a small rectangular white marble plaque to Martha Hughes, d.1821, aged 17.
Stained and painted glass: The N chamber E window contains the famous 'Jesse Window', a large, and remarkably accomplished Tree of Jesse, dated 1533 and widely regarded as representing the apogee of the early Tudor North Wales school of glazing. The fragmentary remains of what presumably formed the figurative glass of the chancel (S chamber) E window, are contained within the N chamber W window; amongst the fragments is a date inscription of 1508. This glass was found c1830 hidden in a local farmhouse; presumably it had been removed during the Civil War.
The S Chamber has good figurative glass to its 4-light window, 2 scenes per light; those to the upper show scenes from Christ's Passion, the lower show Acts of Charity. The glass commemorates Margaret, wife of Thomas Hughes of Ystrad, d.1854. To the W of this is a 4-light window with good figurative glass showing 8 scenes from the life of Christ; the glass commemorates James Vaughan Horne, d.1848.
The N chamber N wall has four 2-light windows with fine figurative glass dedicated to the memory of Thomas Hughes of Ystrad, d.1881; scenes following the Resurrection. To the W of these is a further window with fine figurative glass of c1900 showing Christ amongst children.