St John's has an early 12thc. nave to which three-bay aisles were added c.1170-80. One of the original nave windows is visible on either side. A clerestorey was added in the 14thc. The nave doorways are both 14thc., the N now leads to a modern octagonal parish room, while the S is under a porch. The chancel is 12thc. too; again one of the original windows is visible on the N, with a two-bay N aisle added at the same time as the nave aisles. It is possible, as Thorneycroft suggests, that there was a similar arrangement of the S side, but if so it is difficult to see why this was entirely rebuilt in the following century whereas the N arcade was simply augmented. At some time in the 13thc. the N aisle was extended by one bay, and a three-bay S aisle added. This is now a chapel, while its counterpart on the N is taken up by the organ and vestry. The chancel was lengthened in the later 14thc., and a crypt added under the extension. The west tower is 14thc. work, and refaced in its upper parts. It has an octagonal ashlar spire with three sets of lucarnes. There was a complete restoration in 1863, by Slater of Carlton Chambers, London. This included the replacement of the chancel arch and east wall, the rebuilding of the nave clerestorey and the N nave arcade, the rebuilding of the NE corner of the tower and west end of the north aisle, and the rebuilding of the south aisle wall on a new line. It was at this time that the original nave and chancel windows were rediscovered. Construction of the church is largely of ashlar. The Romanesque features recorded here are both nave arcades and the chancel N arcade.

In 1086 Kingsthorpe was held by the king. No church was recorded at that time, and it is usually assumed that it was founded from St Andrew's Priory, Northampton. At some time after c.1160, St Peter's Northampton, along with Kingsthorpe and Upton as dependencies, was granted to Henry, son of Peter by the Prior of St Andrew's. Until 1850 St John's, Kingsthorpe and St Michael's, Upton were chapels of St Peter's Northampton, but both received parish status at that date.

Benefice of Kingsthorpe with St David's Northampton.

The chancel arcade is stylistically simpler and earlier than either of the nave arcades, and of the two last, the N must come before the S. It is assumed that all belonged to an extended campaign of expansion between c.1160 and c.1180. The S nave arcade capitals, the latest of the campaign, should be compared with work at Croughton; not for a workshop connection but for a similar unusual treatment of a fairly common type of capital.