The church stands in a highly unusual position in a loop of its northern parish boundary, several hundred yards away from the hamlet of Throapham on the B6463, and only a quarter of a mile from the parish church at Laughton-en-le-Morthen. The church is no longer used for services. It is kept in repair by the Churches Conservation Trust and usually locked.

The building consists of a Perpendicular tower, a S porch and a chancel that were both rebuilt in 1709, and a much older nave, with aisles, dated to the late 12thc and early 13thc. Only the waterleaf capitals of the round-headed doorway are clearly Romanesque.

The church, a chapel of Laughton-en-le-Morthen, lay within St John's Field, one of the three ancient open-fields of Laughton. In 1631 Roger Dodsworth noted that there had once been a great summer fair which had attracted large numbers of pilgrims to the church.

A parish magazine cover for Laughton in 1913 includes 'Thorpe Saint John's' in its title.

Ryder (1982) observes that the N, S and E walls of the nave are only only 2ft. 2ins. (0.65m) thick, and suggests that they survive from an aisleless church of pre-Conquest or 'Overlap date'. He proposes that this was enlarged by the addition of aisles and the rebuilding of the chancel c.1200. Harman and Pevsner (2017, 664-65) concur with this dating, and suggest that the chancel arch belongs to the same campaign.

The doorway is not in situ (Ryder 1982, 98), so it may comfortably be dated before the arcades. The arcades have been included for comparison with several other local churches that had arcades added in the late 12thc or early 13thc. The arcades were shortened when the tower was added (Ryder 1982, 97).

The two waterleaf capitals on the doorway have details that are reminiscent of capitals at Roche Abbey, where in the SE pier of the crossing, on the side in the presbytery, a capital has an extra leaf in the gap between the waterleaves, and it is scalloped like the R capital at Throapham. Further round that pier to the R, another capital has the remnants of two circular motifs with holes. The stone at both places is so worn that these comparisons may seem uncertain, but extra ornament of waterleaf capitals is unusual, and a pair with similarities more so.