The small and simple Anglo-Saxon building is distinguished by its "remarkable" and extensive set of wall paintings, dating from the early 12th century and rediscovered more than 700 years later.

The ancient village of Clayton, situated where the main route from London to Brighton crossed an east–west track at the foot of the South Downs,[1] existed at the time of the Domesday survey in 1086, when it was called Claitune or Claitona.

[2][3] It was at the southern end of the parish of the same name, which covered 1,414 acres (572 ha) of mostly rural land running north (and downhill) from the summit of the South Downs.

[10] The lychgate at the entrance to the churchyard was built in the early 1920s by Philip Mainwaring Johnston[14] and serves as Clayton's war memorial.

A Falklands War casualty is commemorated, and there is also a military grave from that conflict in the churchyard, where American theatrical producer Marc Klaw is also buried.

[5] The most famous feature of St John the Baptist's Church[8] is the array of well-preserved and ancient wall paintings in the nave and on the chancel arch.

[16] The examples at Clayton have been described as "some of the most important in the country",[5] "remarkable",[3][11][19] "a fine set",[13] "amazing",[1] "unique in England for their extent, preservation and date",[17] and "graphically representing ... the terrors of Judgment Day".

[24] The murals cover the chancel arch and the east, south and north walls of the nave,[13][19] and were uncovered between 1893 and 1895 when Charles Eamer Kempe was restoring the interior.

[5][8][19] Like the other Lewes Group paintings, they feature a very small range of local pigments in shades of yellow and red (leading to the nickname "bacon-and-egg").

[1][16] The main subject of the murals is the Day of Judgment, making them an early example of the "Doom" paintings seen in medieval churches across England.

[5][15] Pevsner noticed that the figures had characteristic features: "extremely long and lean, with heavy ... garments, exceedingly small heads ... [and] strange headgear".

[26] On the north wall of the nave, a procession (led by bishops) approaches the Heavenly Jerusalem, watched by angels and saints, and the defeat of the Antichrist.

[18][26] Scenes on the south side include angels, one of the Four Horsemen of the Apocalypse, worshipping saints[3][26] and another procession, this time of the damned: in this dramatic composition, "a spike-heeled devil riding a large beast separates the doomed from the blessed".

[5] The structure dominates the nave through its sheer height, the use of massive square stone blocks with a smooth, plain finish,[30] and the three 10-inch (25 cm) moulded shafts on each side.

[10] The nave formerly had a pair of porticus-style side chapels, but little trace of these remains—although blocked windows and fragments of archways and gabled roofs have been visible since 1918, when they were excavated.

[37] The parishes of Clayton and Keymer, previously separate legal entities, were united from 25 July 1978 by means of an Order in Council.