St Mary's is a large church, now consisting of chancel, N vestry, S chancel chapel, N transept with E chapel, S transept with W chapel, crossing with tower and spire, and aisled nave. Remains of the primary nave, rubble-built with herringbone courses, are 11thc. or earlier. The chancel arch is late 11thc. or early 12thc.; there is documentary evidence, and some archaeological evidence, for a big W tower existing by the 1140s. The church was grandly remodelled during the second half of the 12thc. The tower on crossing-arches was raised over the E part of the former nave, large new transepts and chancel were built, and there was probably a S aisle. A plain round-headed single-splayed window remains in the W wall of each transept. The belfry openings, one in each face of the tower, were remodelled in the 13thc. but retain the plain square jambs and under-chamfered abaci of the 12thc. openings. It was stated in 1871 that `the rough traces of three or four Norman windows in the N wall [of the chancel] were brought to light, when the plaster was stripped. All the masonry of these windows had been apparently removed' (Notes of an Excursion..., 34-5).

The spire was added in the 13thc., and the nave was largely rebuilt in the early 14thc. A harsh restoration in 1870 involved renewal of some of the Romanesque detail.

Romanesque features recorded here are the south transept south doorway, and internal doorways to the chancel vestry and the north transept stair turret (these internal doorways are described in section III.1.(ii) to (iv), a string course and a corbel table (largely renewed) on the exterior of the chancel, the chancel arch and crossing arches, interior string courses in the chancel and tower, blind arcading in the tower, and various rest fragments, inside and out.

This was an Anglo-Saxon minster church, given by Bishop Leofric to the new cathedral of Exeter in the l050s. Bishops from the late 11thc. to mid 12thc. used Bampton as a residence, but from the 1150s onwards the church was controlled by the cathedral canons. A late 12thc. arrangement by which a `prebend-farmer', usually a high-ranking ecclesiastic, controlled the appointment of two lesser `prebend-portioners', was transformed in 1220 into three portionary vicarages, which survived until the 1840s. Throughout the later Middle Ages Bampton remained the mother church of an exceptionally large parish, controlling many daughter churches and chapels.

The great size of the late 12thc. church, closer in plan and scale to a small monastic church than to a parish church of the time, reflects its unusual status. The pointed crossing arches, with their simple square orders, may reflect the patronage of the canons of Exeter: it has recently been argued that the nave of Exeter Cathedral had pointed arches (Thurlby, 29), and late 12thc. pointed arches with plain square orders also occur in their Devonshire churches of Crediton, Branscombe and Colyton. In turn, it may be thanks to the influence of Bampton that chancel arches in a similar style occur locally at Clanfield and Standlake, and a tower arch at Broughton Poggs. On the other hand, the elaborate S doorway is probably a product of the Gloucs./Wilts. workshop responsible for Quenington etc. and ultimately reliant on a Reading Abbey workshop (cf. the clasps, the heads and the pierced pellets.)