A large church of local brown sandstone, restored by Teulon in 1865, comprising a W tower (12thc.) with a broach spire, an aisled nave (12thc. and 13thc.) with a clerestorey, and a square chancel (late 13thc.). Chantry chapels have been added to N (14thc.) and S (15thc.) and a sacristy to the NE (Perp).

Horsham is not mentioned in Domesday Book. The W tower and the NW corner of the N aisle appear to be remnants of an earlier church which was substantially rebuilt in the 13thc., probably in 1231, when the advowson passed to Rusper Abbey. Rusper, a nunnery founded by William de Braose c.1200, also possessed the churches of Warnham, Ifield and Selham.