[2] Continually altered and enlarged until the mid-19th century, the church displays every style of architecture from the Norman to Victorian eras,[3] and has been designated a Grade I listed building.

[5] The earliest records of a church at Downton comes from the Saxon era, when the village was owned by the Bishops of Winchester, who built a manor house here.

[6] This early structure, of which there are no visible remains, was the parish church for a wide area, including not just Downton, but some 5,700 hectares (22 sq mi) of land along the Hampshire-Wiltshire border.

This building work included extending the 1147 nave to the east with two further bays, the construction of transepts and a low central tower.

The chancel was built or rebuilt from 1346 to 1352 in the Decorated Gothic style, the tower raised by a further storey and the nave extended with the addition of aisles.

The chancel was built on an unusually large scale and separated from the rest of the church by a screen, likely to accommodate the Bishops of Winchester.

[3] The church underwent the first in a series of major restorations in 1648, when the south aisle was rebuilt in facsimile, including the porch.

One of the most significant events in this period occurred in 1791 when Jacob Pleydell-Bouverie, 2nd Earl of Radnor, funded the heightening of the tower by some 30 feet (9.1 m), so he could see it more clearly from his home at the nearby Longford Castle.

This work included the construction of an additional storey topped by a new parapet, with heavy battlements and corner pinnacles.

[2][3][4][7][8][9][10] From 1812 to 1815, the church underwent further restoration and alteration by Daniel Asher Alexander,[4] who added an unusual brick parapet to the top of the south aisle.

The church was restored on a much larger scale by Thomas Henry Wyatt in 1860, which involved removing the partition between the nave and chancel, lowering the tower to its pre-1791 height (but keeping the Earl's battlements) and the replacement of much of the windows and tracery.

[4] The building is constructed and designed in the traditional cruciform layout, with an aisled five-bay nave, transepts, central tower and chancel.

[5] The west wall of the nave features a large four-light Decorated Gothic window of the Geometrical period (1245–1315) above a Tudor-arched moulded doorway.

The nave aisles feature two-light and three-light windows with chamfers and hoodmoulds, the 17th-century south porch with Tudor-arched doorway sits between the 2nd and 3rd bays.

The north side also has a pointed doorway with continuous moulding and adjoins an octagonal stair turret in its western corner.

The second stage of the tower has a pair of larger round headed window openings in the centre of each face, each one filled with louvre boards rather than glass.

The west window contains glass from 1896 and 1907 by Edward Frampton, depicting the angels Uriel, Michael, Gabriel and Raphael.

The eastern window of the south transept contains glass made by Heaton, Butler & Bayne in 1889 and 1893, illustrating the Annunciation and the Good Shepherd.

The oldest fitting in the church is the fine 13th-century font, made from Purbeck Marble, at the west end of the south nave aisle.

It was replaced in 1870 by a much larger organ built by William Sweetland of Bath, formed of two manuals plus a pedalboard and 19 stops.

Though neither its age nor maker can be accurately ascertained, it is first mentioned in the church accounts in 1735, when Samuel Loveday Bill was paid £2 to repair the clock.