The church bears a very rare dedication to the twin Saints Cosmas and Damian, Christian martyrs of the 4th century.

A church existed on the present site at that time; it was associated with Lewes Priory, which had been given it by a successor of de Watevile in 1093.

[1] The present building incorporates some 12th-century structural elements: the chancel walls[1] and apse[2] date from that time.

[11] The saints are believed to have been twin brothers who worked as doctors in the Roman province of Syria.

[12] The church walls are built of flint in an irregular style reminiscent of crazy paving.

[2] The plan consists of a chancel with Norman-era apse, nave, aisles, and a porch at the south end.

[1] Although the churches at Clayton and Keymer have been connected since their founding,[13] the parishes were not officially united until 25 July 1978 by means of an Order in Council.

English Heritage granted the church Grade II listed status on 21 June 2007.