Inside the porch are war-memorial tablets above window level, and an added 1939-45 memorial tablet in the W wall. The roof has closely spaced rafters. The S aisle S doorway is segmental-headed with prominent voussoirs. It has a C20 boarded door, but on the inner side are battens and strap hinges from the previous door.
The main church has plastered interior walls. The nave has C12 3-bay N and S arcades with low round plastered piers with simple capitals, and round arches. The responds at the E end are square. Round piers at the W end demonstrate that the nave was originally at least one bay longer before the tower was built at the end of the C17. Clerestorey windows have round rere arches, except for the end windows in the S wall, which have square heads. The 5-bay late-medieval nave roof has corbelled arched braces, windbraces, and added tie beams. In the N aisle 3 of the piers have arched buttresses, and trusses that survive the restoration of 1884. Likewise the S transept has trusses earlier than 1884, which are also supported on unusual arched struts supported on the capitals of the piers.
The C19 crossing arches, in C13 style, have an outer continuous order, and an inner order on shafts with head corbels. Beneath the tower is a heavy framed ceiling. Transepts have roofs of closely spaced arched braces, and plastered round arches at the ends of the aisles. The N transept also has a pointed window and a pointed boarded door to the vestry.
The chancel has a boarded wagon roof with moulded ribs and embattled cornice. Wood panelling around the walls, incorporating blind Gothic arches with delicate tracery, is partly dated 1910, and an integral reredos, which also incorporates shields bearing Passion symbols, is dated 1908. The E window has rere arches with ringed shafts.
The square font is chamfered at the angles, stands on a squat octagonal stem and square base, and is late medieval. Late C19 pews have shaped ends. The polygonal wooden pulpit has open Gothic panels. The altar rail has a moulded wooden rail on iron uprights with scrolled brackets.
There are 3 medieval memorials. In the N aisle is a tall early Christian stone with Latin cross and an inscription in Welsh (one of the earliest recorded uses of the Welsh language in a Christian context). Two effigies are in the N wall of the chancel, probably placed there following the restoration in 1884. The early C14 effigy of a priest has his head beneath a gabled canopy and feet on mutilated lions. The effigy of a knight, of c1350, has feet resting a headless animal, probably a dog. The shield is too mutilated to identify the knight, although the effigy has traditionally been identified as Gruffydd ab Adda of Dolgoch.
Other memorials are wall tablets, mostly salvaged from the previous church and reinstated after its restoration. In the chancel N wall is a classical marble memorial to Vincent Corbet (d 1723). The inscription panel has an apron with foliage and winged cherub, an open pediment and an achievement with garland. Further R is a simple classical memorial to Anne Maurice (d 1767) and family. It has an inscription panel, apron, entablature with painted coat of arms and a shallow cambered moulded cornice. In the S wall is Gothic style wall tablet to Lewis Vaughan (d 1877), under a cinquefoiled arch and gabled canopy, with a classically dressed woman in high relief. Next to it is a plain marble tablet to the Rev William Lewis and his wife (d 1716, 1698). Further R is a rococo tablet to Atheluston Owen (d 1731), by Sir Henry Cheere. It has a corbelled inscription panel over a running-dog frieze, and apron bearing an inscription to his wife Anne (d 1766). It is surmounted by an urn against a roundel under a scrolled pediment with achievement. Scrolled wings are further enriched with husk garlands.
In the S transept is a simpler tablet with cornice and apron, to Richard Edwards (d 1785) and family by John Carline of Shrewsbury. Below it is a small brass to Rupert Kettle (d 1908). In the N transept the W wall has a simple brass to William Kettle (d 1930), and in the N wall is a brass panel in a stone pedimented surround to Louis de Saumese (d 1788). In the S wall, a severe classical tablet to Edward Scott (d 1842) has an inscription panel and pediment. Below it is a plain brass to Griffith Evans (d 1923). To its L is a plain small brass to Ann Dafydd (d 1785) with inscription in Welsh.
Several windows have stained glass. The chancel and transept windows form a set and are probably therefore by the same glassmaker. The E window shows Christ in Majesty and scenes from the Passion. The S transept shows the Nativity and the N transept shows the Virgin Mary and SS Peter and Cadfan (all of whom had altars dedicated to them in the medieval church). The chancel S window, post 1944, shows the Adoration of the Magi in conservative style. The W window shows SS Matthew, David and Cadfan, dated 1883. In the S aisle the W window depicts the child Christ, post 1941 by Wippell & Co of Exeter. In the S aisle the small window shows Mary and Jesus, the larger window probably the death of the Virgin.