Christian worship has been offered here on the site of St Mary's Church for over 800 years. We know there was a church on this site in 1155 and the earliest visible craftsmanship to be seen is the font, which survives from the 12th century.
The Church has changed a lot over time with major taking place in nearly every century. The most significant change was in the 18th Century due to damage from a major storm in 1702, when the tower was severely damaged, and in 1774, when the body of the church caught fire.
The interior of St Mary's is distinctive. It is long and low, which creates a tunnel-like effect, due to the continuous plaster ceilings, which cover an unbroken length of some 93 feet and date from 1774 – although the south side roof was renewed in 1979. Extra light is given by the plain and rustic windows in the nave roof. At the centre of the nave hangs a fine chandelier, believed to be 17th century, which hangs from a pretty plaster pattern. The chandelier was converted from candles to gas lamps and subsequently to electricity in 1935 and in the late 1990s reverted to candles.
The aisles are divided from the nave by arcades of nine bays. This is a remarkable number for the size of the church. The arcades are a dominant feature of the church and they stretch for its entire length.
Following extensive renovation work in 2008 the west end of the north aisle has been converted into a vestry/meeting room, which is named after the Shrine of Our Lady at Walsingham. The guardians of the Shrine are the patrons of the living and the Parish has enjoyed close links with the Shrine over many years. Included in the room is a beautiful niche which has a mass of 14th century stone-carving, including leaves and flowers.
Access to the tower staircase is through the toilet by way of a mediaeval door which is bound with iron. This leads to the bell chamber in which six bells hang, the oldest of which dates back to 1415.
There are a number of notable memorials in the church including plaques on the walls and ledger-slabs on the floor. One commemorates the fire of 1774 and is made from 18th century roof lead. Also in the north chapel is a tablet to members of the family of Rev'd Alexander Scott, who was Curate of Burnham for many years from 1808 and, during the time of an absentee Vicar, was also Vicar of Southminster. He was Chaplain on board H.M.S Victory at the Battle of Trafalgar in 1805, and Lord Nelson died in his arms.
Amongst the plate held by the church is a cup and cover, also a paten, made in 1638, an 18th century flagon, also some tasteful 19th and 20th century plate, including a ciborium given in 1977.
The registers of the church date back to 1559 and are held by the Essex County Archives.