The church comprises a nave with a W porch, a W bell-turret, a 13thc. S arcade and a simple two-bay chancel. The plain W doorway has a tympanum in a raised surround.

The church was not mentioned in the Domesday Book, but Eartham belonged to Aldingbourne manor and was held by the Bishop of Chichester. Between 1157 and 1169, Bishop Hilary gave the church to Richard, the chaplain of Chichester, with two houses, five acres of land and specified tithes, Richard undertaking to have mass said weekly for the bishop's brother, Robert. It was restored in 1869.

The chancel arch capitals are closely comparable with those of Stoughton. The Stoughton arch is larger and is articulated with roll mouldings, while that of Eartham is simpler, with unchamfered arches. In each case, however, the inner order is carried on half-columns with volute capitals. Curiously, the capitals of Stoughton seem earlier typologically. They have fat crooks, which do not form proper unified angle volutes but, despite the flounce added on the N side, seem applied to a smooth bell. On the Eartham capitals, the crooks have become stems, which issue proper volutes, with the exception of that on the E face of the N capital which appears to be purely decorative, and is descended from a type of 11thc. capital represented on the Sompting W tower. The Stoughton and Eartham capitals can be datedc.1100. The capitals are usually compared with Chichester choir caps.