Interior
The nave has scribed plaster walls and a 3-bay collar-beam roof on corbelled brackets. The 2-bay N arcade has C13 style round pier and responds, moulded capitals and pointed arches with 2 orders of chamfer. A wooden balustrade between arches separates the Bulkeley aisle from the nave and has a gate at the R end allowing the worshippers to proceed to the chancel for communion. The 3-bay S arcade has C14 style octagonal piers with moulded capitals, and arches with 2 orders of hollow mouldings. The segmental-headed tower doorway has a boarded door with iron studs. The N aisle has a faceted roof with moulded ribs, square foliage bosses and an embattled cornice. The S aisle, which is faced in brick and painted white, has a 3-bay arched-brace roof on heavy shafts and corbels. Its S windows have broad colonettes.
The steeply pointed chancel arch has 2 orders of continuous chamfer. The chancel has a 3-bay collar-beam roof on corbelled brackets. On the S side is a pointed arch with continuous chamfer, to the organ chamber, and a doorway to its L with similar detail. The sanctuary has a diaper marble floor added in 1902 and a wooden reredos with blind ogee-headed arcading, brattishing, and central mosaic incorporating an IHS monogram. The organ chamber is faced in brick and painted white.
The font has an octagonal bowl with 2 ogee-headed panels to each facet, moulded stem and base, and a marble-lined bowl. Pews and choir stalls are simple late C19 work. The wooden pulpit, dated 1898, is a polygonal with a panelled front, on a low round pedestal. Spanning the chancel arch is a low wall in imitation of a screen base.
There are numerous memorials, some of which were salvaged from the earlier church on the site. In the centre of the chancel N wall is a large wall tablet to Henry Whyte (d 1728) with double inscription panel framed by pilasters with scrolled sides, apron with low-relief cherubs, elliptical pediment with keystone, achievements to the R and L and surmounted by a bust in the centre. To its R is a Gothic memorial to Sir Robert Williams (d 1830) and his wife Anne (d 1837). An inscription panel is framed by a quatrefoil frieze across the base, panelled polygonal shafts, thinner to the upper portion flanking a canopy of nodding arches, surmounted by a rich frieze. On the L side of the N wall is a smaller Gothic wall tablet to Ann Williams (d 1858). It has a pointed inscription panel within a surround decorated with low-relief foliage and 2 angels, under a crocketed gable. A lower panel by White of London is in a different style, and comprises crossed torches and a wreath.
The E wall of the chancel has a small memorial to Jane White, comprising inscription panel with slate surround, apron, entablature and achievement. A simpler tablet is to Eliza Wilmot (d 1887), and a brass plaque to Robert Williams (d 1865) is by Hart & Son of London.
In the nave W wall is a wooden plaque over the tower doorway commemorating the completion of the new church in 1845. To its R is a memorial to Emma Jones (d 1786), comprising inscription panel over an apron with coat of arms, and beneath a steep pediment with urn. Below it is a white marble panel with grey marble surround to Elizabeth Jones (d 1813). Further R is a memorial to John Hampton Hampton Lewis (d 1843) by C.M. Seddon of Liverpool. It has a tapering panel, scrolled sides over a moulded base, and pediment with achievement. On the L side of the tower doorway is a simple marble tablet to Justina Morgan (d 1851) and a simple tablet with moulded surround to Joseph Hampton Hampton (d 1878).
In the nave N wall are 2 plain panels commemorating Charles Lewis (d 1844) and Owen Owen (d 1857). A slate panel to William Dalton (d 1763) has an inscription below a coat of arms in low relief. In the S aisle E wall is a large brass plaque commemorating all the members of the Hampton and Hampton-Lewis family of Hennllys who were buried at Llanfaes between 1460 and 1946. Below it is a triple brass plaque to 3 members of the family who died in the period 1906-12. In the N aisle is a large brass plaque commemorating Thomas James Williams Bulkeley (d 1887) by Matthews & Hodgson of London. It comprises 3 Gothic arches with central inscription panel and guardsmen under the outer arches. To its R is a Gothic wall tablet with inscription panel framed by a cusped arch, foliage cornice and crowned by a frieze of flowers.
Several windows have stained glass. The E window depicts the Resurrection. The chancel S window has a re-set figure of St Peter, possibly from the older church. In the chancel N wall is the baptism of Christ. In the S aisle, the window near the E end depicts the Nativity and resurrected Christ in one pair of lights, and SS Catherine, Nicholas and Maurice in the other pair, the latter dated 1964 and probably by Martin Travers (the monogram is partly obscured). In the window near the W end the L-hand pair of lights depicts Christ as the Good Shepherd, by T.A. Gibbs and W.W. Howard, and the R-hand pair the New Testament scene 'Suffer little children'. The W window has 2 angels. In the N aisle a commemorative window on the W side has 3 angels and 2 earthbound mourners, dated 1884 by Ward & Hughes of London. The window on the E side, dated 1885 and probably also by Ward & Hughes, shows the Crucifixion.