St Mary's, Witney, is a large cruciform church with a fine central tower and spire, visible from afar and dominating the S end of the Green at the centre of this country town. Mostly of coursed limestone rubble, the church now comprises a chancel, an aisled and clerestoried nave with a NW chapel and a two-storeyed N porch, and clerestoried transepts with chapels and W aisles. The late 11thc. or early 12thc. church probably consisted of aisleless nave and chancel, of which blocked single splay windows survive high in the nave walls. Fragments of string course also survive, formerly on the nave exterior but now interiorised in the aisles. There is only tenuous evidence of an early central tower. It is more likely that the thick W wall, now ostensibly 13thc., is the remains of an early W tower, similar to that excavated at Bampton. If so, the nave retains its original dimensions. The four-bay N aisle and porch were added in the late 12thc., and the latter has outer and inner doorways with round-headed arches, the outer possibly rebuilt. There are a number of re-used fragments of Romanesque masonry, including chevron and a single beakhead.

Although the existence of a previous church seems likely, the earliest unequivocal evidence of one is the survival of blocked single-splayed windows of late 11thc. or 12thc. type high in the nave of the existing building. The ecclesiastical parish was large, but there is no evidence of a minster church at Witney as there was at Bampton and Minster Lovell.

The church was first documented in 1162 when Henry of Blois, Bishop of Winchester, granted it to the hospital of St Cross. The latter's ownership was confirmed in 1189, but by 1211 it belonged to Hugh of Gayhurst, chancellor of the diocese of Winchester. Peter des Roches, bishop of Winchester and confidant of King John, regained it in 1212 when the bishopric was taken into the king's hands, and he and his successors held the patronage thereafter. Henry de Blois is known to have stayed at the Bishop's Palace, the footings of which were excavated in the early 1990s, close to the E of the church.

The VCH refers to numerous re-used fragments of 12thc. masonry, including chevron and a beakhead, that were found in the S wall of the chancel during restoration in 1866. (The chevron could perhaps be that visible outside, although the whereabouts of the beakhead is now unknown).

A piscina or stoup, now partly covered by the raised floor, remains in the S doorway of the chancel, also referred to by Wheeler (2013). The cavity of the stoup is within the L jamb of the doorway, pointed on the outside and rounded within. It is not a convincing Romanesque stoup and is not described here.