At its heart is the ancient nave of the church, which was built by the Benedictine monks of St Albans Abbey c1080. The north wall of the nave, including arched doorway and windows, retains distinctive Norman details. A chancel extending the nave was joined in the 15th century, and enlarged in 1632.
A neo Norman brick tower with decorated stonework was added to the south of the nave in 1828. The south aisle, of Kentish ragstone, was added in 1868 and the original south wall of the nave was replaced with an internal arched arcade incorporating one large, squat red marble column. In 1880 there was an extension of the chancel and sanctuary to its present size, and the organ chamber was added on the north side.
Unusually, the church houses a large number of funeral hatchments and there are other monuments internally. The peaceful churchyard many memorials including some large chest tombs and timber burial markers. At the west end of the church is a monument to John Sharpe, comprising a large urn mounted on a base under a heavy arched baldicchino. North of the church, there are a series of obelisks to the Grove family, all of the same design and decorated with putto heads. To the north east of the church is a memorial to Sir Simon Haughton Clarke in the form of a tall Gothic monument with octagonal lantern on octagonal plinth. These latter memorials are listed Grade II.
St Mary's offers a warm welcome to all.