The church is substantially late medieval and Victorian, retaining no evidence of the Norman structure to which the font may have belonged.

Warnham is not mentioned in the Domesday Book, but before 1204 William de Braose gave the church to Rusper Nunnery (confirmed by Bishop Seffrid II, 1180-1204, VCH vol II, 63ff). Rusper Nunnery also held the churches of Ifield, Selham and, from 1231, Horsham.

The medieval dedication is noted in a will of 1505 (Sussex Record Society, 45, p.296).

The font is of a simple type found frequently in Sussex and neighbouring counties which seems to have been popular over a long period, extending into the 13thc., and examples are difficult to date. The majority, however, seem to have been produced in the second half of the 12thc., and the Warnham font can be tentatively assigned to that period.