The church has chancel, crossing tower and S transept, and nave with S porch. Of the original 12thc. crossing only the E and W arches survive. The tower was completely rebuilt in 1876 and the current S transept dates from the early 20thc. The chancel was altered in the 14thc. but probably retains some of the original 12thc. walling. The nave has blocked 12thc. round-headed windows, one on the N and one on the S wall. In the exterior walls are some reset moulded fragments which could be 12thc. Simple Romanesque sculpture is found on reset voussoirs in the chancel arch. The church is built of flint and rubble, uncoursed apart from the nave.

Prior to the Conquest the manor of Pirton was held by Archbishop Stigand. At the time of DS is was held by Ralph de Limesl, whose family held the manor until the end of the 12thc. Ralph de Limesl gave the church and tithes to the Priory of St Mary, Hertford, which he had founded as a cell to St Albans. The priory held the advowson until the Dissolution.

VCH dates the tower arches to 1130.

Pevsner records that the transepts were originallly apsed.