St Mary's has a nave with a two-bay N aisle without any windows and a S doorway under a porch. The square-ended chancel has a N vestry and organ chamber, and there is a W tower with a broach spire with two tiers of lucarnes. An 11thc. window in the W wall of the nave indicates an early date for the core building. The S doorway dates from the early 13thc., and the N arcade and tower are slightly later. The S porch is dated 1663, and at that date too the S nave wall was rebuilt. The clerestoreys to N and S were presumably added at that time too. At some point, probably in the 15thc., the chancel fell down, and the E nave wall was rebuilt without a chancel. Until the new chancel was built in 1902 on the old foundations, St Mary's was claimed to be the smallest parish church in England. Construction is of stone rubble and ashlar. The church boasts an exceptional font of the 1120s, which is the only feature described here.

Wansford does not appear in Domesday. A charter dated 664 confirms a grant of land there to Peterborough Abbey, but this is generally thought to be a post-Conquest forgery. It was certainly part of the Soke (or jurisdiction) of Peterborough Abbey in the relevant period.

Chapel of Ease to Thornhaugh, St Andrew. Now part of the benefice of Thornhaugh and Wansford.

The font was brought to the church from Sibberton Lodge, where it had been in use as a cattle trough. It is unlikely, therefore, that Wansford was its original home, especially as a broken font bowl was found during excavation for the rebuilding of the chancel in 1902. This was used to make the base for the rescued font. The narrative treatment is interesting in that it consists of figure scenes separated by foliage motifs. The Baptism of Christ is normal for a font, and the scene of fighting warriors, suggestive of man's battle against sin, has iconographic parallels elsewhere e.g. in work of the Herefordshire School. The scenes involving Christ, St Peter and the Angel, and St Paul are unusual. They may refer to an earlier dedication of the church although there is no other evidence for this. According to Pevsner (1968), Zarnecki has supported a date of c.1120, and the present author accepts this too.