Seaford church has a W tower, an aisled nave with two-bay arcades and a S porch, a non-projecting transept, a large chancel with a polygonal end and a N chapel. The Perp tower seems to have been erected within the W bay of a Norman nave, but the W doorway is neo-Norman rather than Norman. Herringbone masonry suggests that the N aisle is of Norman origin, but the present two-bay nave arcades, clerestoreys and corbel tables appear to date from the early 13thc. One capital in the S arcade is historiated, with the Baptism of Christ, the Harrowing of Hell, Daniel in the Lion's Den, the Massacre of the Innocents, and the Crucifixion.

Seaford was one of the Cinque Ports and could afford a large church.

Several campaigns of repair and restoration were undertaken in the 19thc. and early 20thc. The most significant was by the architect John Billing in 1860-62 (Brighton Gazette, 10 July 1862, 7). Billing extended the nave, with flanking transepts, by 26 feet. A new chancel was provided, with a vestry on its S side, and the aisle roofs were lowered. The W tower was restored in 1886.

The large St Michael fragment is thought to have been dug up in the churchyard in 1778, when 'the site of the old burnt chancel was explored' (SNQ 1940-41). The smaller fragment was found during work of the 1930s (?) by W. H. Godfrey, who was responsible for mounting the reliefs in their present position in 1939-40 (Crawley & District Observer, 1 June 1940, 2).

The 15thc. W doorway was replaced by a new entrance by the architect William Woodward in 1894-95. During the work, Woodward found a base, capital and part of the jamb shaft of the earlier doorway. A photograph of 1943 in the Historic England Archive (red boxes) depicts these elements amongst a collection of other loose fragments. The caption on the back of the photograph reads: 'Shaft of respond of West Door now in Barbican Museum, Lewes'. Two faces of the capital were carved with sheathed cones and plain shields. It retained its necking and was balanced upon three sections of an engaged shaft, stacked upon a bulbous base.

Stylistically, the St Michael fragments are closely related to the Chichester Reliefs (c.1125-35). It has been suggested that they came from a tympanum. Taylor suggested that this tympanum was located at the west end of the church where, in 1813, Frederick Shoberl noted 'a spacious entrance under a pointed arch, above which are the remains of another circular form, the intermediate space being walled up'. For more on the W doorway, see History.

The form of the font (a square bowl on five columns) suggests that it might be of 12thc. or 13thc. origin, although its various elements have been replaced or renewed over time (for photograph see: Drummond-Roberts 1935, 74). It was not recorded.