The interior of the church is grandly spacious, with whitewashed walls and clear of fixed furniture. A later C15 roof of alternate hammer-beam trusses and moulded intermediate principal tie beams supporting the low-pitched roof supported by moulded purlins and ridge piece, with the intersection bosses carved with leaf and rosette motifs. The wall posts below the ties stand on stone corbels. Wide arches to the crossing, with triple roll imposts separated by hollow mouldings, rising to small circular capitals and the arch over with a bracket-moulded order. The crossing is stone paved, carried into the transepts. Six C16-C17 trusses in Gothic style infilled with tracery above the tie beams, the end trusses arched over the heads of the transept windows. Two steps lead into the chancel, passing through a rood screen of 1531, much restored in 1940. The short chancel is of 2 roof bays, with further steps to the high altar. Whitewashed walls and stone paving. On the S side, a small arched piscina and triple sedilia with crocketed canopies. The tower has a transverse oak bellframe with 3 bells. The tower roof contains some reused moulded timbers.
Fittings: the chancel screen of 1531 has 3 bays either side of central doors. Bar-stop chamfered sill and moulded posts supporting the roof loft, mostly of 1940, with excellently carved bands of undercut oak swaying scrolls based on original evidence. The tower screen is a robust post and panel partition with the upper register of turned balusters. Three-plank studded door with a curved head. Font: diminutive panelled step carrying a modern octagonal bowl of oak. Organ: the gift of the Glynne family of Glynllifon, 1932, originally hand blown, with an end console. Pulpit: c1700, octagonal and panelled, a scrolled beast on the top panel. In the chancel, fine choir stalls of c1500, 4 each side returning as 3 backing on to the rood screen. Small arms with carved head terminations and misericords supported on traceried brackets with leaf supporters. The book desks have linenfold panelled fronts between moulded muntins, poppy-head terminals, and facing into the axial passage, the Glynne double-headed eagle crests.
Glass: seven C19 roundels in the E window, the Glynllifon glass of 1540-1558 has been removed.
Monuments: in the chancel (a) Chest tomb in the NE corner. Shallow carved sides and capstone, carrying armorial bearings of William Glyn de Lleiar, knight, d.1609, the side panelling with quartered arms superimposed. Above, (b) William (Glynne de Lleuar) d.1609, kneeling in front of a reading desk, 7 children behind, set in a corniced panel, inscription between supporting consoles, and arms on a cartouche over; (c) White figured marble panel with pilasters supporting a broken cornice, putto on apron, to George Twistleton of Llyaer (m to the heir of William Glynne of Lleiar), d.1714, his sister added; (d) Black marble tablet by Spence of Liverpool, with white panel with cornice and acroteria, to the Rev Hugh Williams, vicar, d.1833. On the S wall (e) a black marble tablet with white marble inscribed panel and cornice, to Rev John Williams, d.1809. In the N transept, (f +g) two tablets of white marble on black slate, to John Williams, d.1877; (h) Soloman Williams, d.1848 a Methodist. Also various brasses of the Williams family of Brynaerau, and a Lleuar brass to William Glynne of Lleuar, d.1633 in a still medieval style. At the NW end of the transept (i) a ledger raised on square balusters, to George Twistleton of Lleuar, d.1667, carved with inscription and arms, another slightly raised ledger before it (j) to Rev Philip Twistleton BA, d.1700 with his sister, and (k) a further ledger slab on the floor under to a later William Glynne, d.1660, with his arms and inscription. In the S transept, set low on the wall, (l and m) 2 tablets to Elizabeth Williams of Nantcall, d.1760 and Thomas Williams, also of Nantcall, d.1794.
Furniture: in a glass case, Cyff Beuno, the hollowed trunk chest of St Beuno, bound in iron in the C17 and provided with two locks. It was originally located at the E end of the chapel.
The Chapel of St Beuno is approached by an external passage from the tower, which was at one time used as the village lock-up. The plain walls corbel inwards to support the large slab ceiling, above which the vault is corbelled. Stone lintels at each end, and one small window each side. The chapel is of 4 roof bays, the trusses carried on wall posts on corbels. The walls are whitewashed and the floor stone paved. One step only differentiates the E end. A vice stair in the NW corner provides access to the roof. On the S wall at the E end a trefoil headed piscina, with an aumbrey in the E wall. Set in the floor the 'Maen Beuno' a boulder inscribed with a simple cross of C7-C9 date, found at Glan Beuno y Bont Newydd, where it had served as a boundary marker. The tomb of St Beuno was here until moved in 1793.