The interior is plastered and the windows have segmental moulded freestone rere arches. The nave has 4-bay arcades, in which the central piers on each side are octagonal and the remainder are round. The nave has a clerestorey sill-band and an 8-bay roof of arched-brace trusses on corbelled wall posts, of which alternate trusses also have bracketed tie beams. Aisle roofs have corbelled brackets. The chancel arch has an outer order of ringed shafts of polished black stone and foliage capitals, and inner order with similar detail to corbelled shafts, and double-chamfer in the arch. The chancel has a roof of cusped arched braces on corbels, in 3 unequal bays. The S aisle and chancel have double-chamfered arches to the organ recess. The chancel also has a pointed S vestry door with studs and strap hinges. On the S side is a cusped piscina and roll-moulded jambs of, possibly unfinished, sedilia. The N side has a corbelled aumbry.
Re-set in front of the chancel arch are communion rails of twisted iron uprights and scroll brackets, and a moulded wooden handrail. Under the chancel arch is a re-set reredos, of which the central portion has cusped-arch panels and painted cross and Evangelists with central gable and crocketed finials. Outer sides have plainer cusped panelling.
The square freestone font is rounded at the angles, and has round panels with Christian motifs in relief. It stands on a round stem with detached polished stone shafts at the angles, to a moulded base, and polished stone plinth. Simple benches have shaped ends with low-relief foliage in small panels. The large polygonal wooden pulpit stands on posts, has 2 tiers of panels enriched by foliage in low relief, and carved emblems of the Evangelists below the cornice. A low chancel screen attached to the pulpit has similar detail and raised inscription band. The wooden reading desk has a large wooden sculpture of St John.
All windows have stained glass. In the chancel, the N windows depict Crucifixion and Resurrection. The E window, post 1881, depicts the Ascension and other smaller scenes. On the S side the single window shows Jesus at Emmaus.
In the S aisle, beginning at the E end, is Christ as a shepherd, John the Baptist and the Baptism of Christ, post 1887; Jairus' daughter, by Lavers & Westlake of London, 1894; Child Christ, post 1893 also by Lavers & Westlake; and 'suffer little children', post 1907. The W wall of the S aisle depicts the anointing of David as King of Israel and the infant Samuel in the Temple, post 1905. In the nave, the main W window depicts the calling James and John to become disciples of Jesus. In the small windows, the L-hand shows St Peter, post 1914, and the R-hand, above the font, has a semi-abstract interpretation of Baptism incorporating a font with IHS monogram, dove and bell motifs, by Celtic Studios, 1974. In the N aisle, the W window depicts Faith, Hope & Charity, post 1911. In the N aisle, from the W end, is the Sermon on the Mount, by Lavers & Westlake, 1908; the Annunciation by E. Frampton, 1899; and Christ teaching Nicodemus. The aisle E window depicts SS Peter and Paul, post 1886.