This church was built on what was originally a small sandy island west of the old Saxon town. Leland says that there was at that time a nunnery there but this is not confirmed. Certain it is that the Danes raided the town a number of times, and that the Normans built banks, or walls, to prevent flooding here, and erected the first church of St Mary of which building some work still remains inside the west end. The church has had an unusually stormy history. It was severely damaged by French attacks in I217, and again in I457. In I578 an earthquake caused damage to the building which may have been the reason for the collapse of the central tower in 1667. The church was empty and derelict for some time, but was restored in recent years by the Friends of St Mary's and services are still held there from time to time.

Early documents belonging to the church date from 1311, and the registers from I474. These are now housed for safe keeping in the County Archives Office in Maidstone. The church contains some interesting remains of early chantries, including the ruins of an altar in the Jesus Chapel. The chancel has an unusually high aumbry in the north wall, believed to have once contained a Latine Cross in which was a relic of St Bride's heart incased in gilt. There are also some quaint epitaphs on tombstones and memorials and several escutcheons, including one of Charles II. The church possesses one of the four floreated crosses in Kent, dating from about 1333.