Church nave has C15 arch-braced roof with small cusped wind braces. N aisle (1880's) has lighter roof in similar style; elongated octagonal piers to arcade of three bays; wooden panelled altar and reredos to E. To N of chancel, organ chamber/vestry; to S entrance to Gwydir Chapel. At entrance to chancel, late C15/early C16 lofted rood screen, one of finest in Wales. Loft has vine-trail rail, and parapet with vaulted and pinnacled niches; parapet on bressumer with vine trail and oak-leaf and acorn bands. Twelve bays to screen with open traceried heads (one with instruments of Passion, one with pigs eating acorns) and canopies with vaulting and panelled soffit, with to W, straight-sided pendant arches. At centre, doorway with square frame and cambered head. Some open traceried panels in wainscoting flanking doorway. Stone stairs to N date from C19 restoration. To W of nave, C19 wooden panelling to tall round-headed tower arch.
Gwydir Chapel: interior retains C17 fixtures and fittings in characterful 'Artisan Renaissance' style. Very low-pitched camber-beam roof panelled with decorative bosses, heraldic shields, date '1634', initials 'I:W' and 'R:W'. To W beam supported by two square posts. Stone flagged floor in alternating slabs of grey slate and brown lias stone. To N, broad arch to body of church with wooden panelling and door with unmitred mouldings; wooden sculpture of eagle over door. Panelling to walls (circa 1.5m high) with pierced and traceried upper panels. Stalls with pierced fronts to round-headed arches, and finials in the form of heads. Lectern with front similar to wall panelling; wooden communion table with turned legs. Low stone table on which is alabaster effigy of infant (Sydney Wynn died 1639). Near entrance from churchyard, fine C13 coffin, said to be that of Llewelyn the Great, with sunk quatrefoil panelling. Effigy of knight, said to be Hywel Coetmore, (circa 1440) plate and mail armour, dog at feet.
On S wall monument to Sir John Wynn and his wife Sydney; two enriched obelisks with heraldic finials, inscribed oval bosses and cherub heads below; behind obelisks, tablet with angel head and skull and crossed bones. Near NE corner, marble tablet (by Nicholas Stone) in crude outer frame records history of chapel. Below tablet, rectangular engraved brass with three-quarter portrait of Sarah Wynn, died 1671 (by William Vaughan) in engraved cartouche, with winged cherubs etc. Round walls, lozenge-shaped brasses with portrait heads of Sir John Wynn, died 1626, Sydney Wynn died 1632; Sir Owen Wynn died 1660; Katherine Lewis died 1669; Mary Mostyn died 1653 (signed Silvanus Crue).