It is possible that a church has stood in Great Bedwyn since the 10th century. Latin gospels that have survived from this time (now housed in a museum in Switzerland) proscribe that tithes should be used for 'the sustenance of God's servants at Bedwyn'. It is also recorded that in A.D. 905, The Bishop of Winchester, Alhund bought land in Great Bedwyn to build such a church. It is known that there was a church standing by 1066, and although the location was not recorded there are some substantial Saxon foundations under the current 12th century church. In 1086 the church belonged to Bristoard, the priest, who was derived it from his father. The church lands were documented as one and a half hide (the whole of the Bedwyn estate covered 80). In 1091 its revenue was given to Osmund, The Bishop of Salisbury Cathedral as an endowment of Bedwyn prebend. When the prebendary was dissolved in 1543, the estate and jurisdiction was passed to the Prebendal manor (held by The Duke of Somerset) and in 1547, to Tottenham Lodge and House. The land of the Prebendal manor was sold to the Crown in 1950 and advowson transferred to the Bishop of Salisbury.
In the Middle Ages several chapels came under the church at Great Bedwyn.
Currently within the modern day Great Bedwyn parish, was the manorial chapel of Crofton Braboef which was first mentioned in 1317. Chapels of ease also existed in East Grafton, Marten, Wilton, Little Bedwyn, Chisbury and Knowle (all of which now fall outside the current parish boundaries of Great Bedwyn). Only Little Bedwyn and Chisbury chapels remain standing today. Little Bedwyn became a separate parish in the 16th century and the Great Bedwyn parish shrunk further during the 19th century as new churches and districts were established at East Grafton and Savernake Forest. Currently Great Bedwyn Church is part of the Savernake Team, and forms one of 11 parishes under the Diocese of Salisbury.
The church, which was dedicated to St. Mary in 1405, is built from ashlar and flint with ashlar dressings. By the 12th century the church was already a large building: The aisles date from this period. In the mid to late 13th century the chancel was rebuilt using Chilmark stone. The transepts and crossing (probably replacing an earlier tower) were built in the early to mid 14th century and in the 15th century, the clerestory was built and the roofs and aisles altered. The structure of the church was much restored and modified during the mid 19th century so that none of its 12th and 13th century architecture is apparent from the exterior. The modifications included an interior refit and removal of 18th century galleries. The 14th century chancel screen was moved to the north aisle by 1894, removed altogether around 1905 but then installed once more in 1975. The Victorian refurbishment uncovered some frescos on several of the internal walls featuring figures of knights, saints and bishops believed to be dated (by the clothing) to the 14th century. Soon after discovery, the frescos were painted over for preservation. In the same period, work on the buttresses uncovered stone coffins imbedded into the walls contemporaneously described as of Early English character. A fragment of a lid of one coffin's bore the symbol of the Knights Templar.
Now held in the British Museum, locally produced pavement tiles from the church include a pair depicting a Knight Templar fighting a Saracen. Copies of the original 12th or 13th century tiles remain in the church. In the churchyard is a preaching cross, parts of which date back to the 1300s.
The church tower houses seven bells with the earliest dating back to 1633. Collections for the bells have been recorded as far back as 1405. The ring is one of the heaviest in Wiltshire registering four and a half tons. The arches in the south transept contain the memorials to two members of the De Stokke family: Sir Adam De Stoke a crusader who died in 1313, and opposite, Rodger de Stokke, his son who died 1343. The church also contains a memorial (c.1590) to Sir John Seymour (1476-1536), father to the Lord Protector, Duke of Somerset and Jane Seymour who became Henry VIII's Queen and father of Edward VI. The church also holds the remnants of a stained glass window from Lady Jane's home Wolfhall, brought to the church in 1901. The church plate, which in the early 15th century was rich, including plates, books and vestments is now reduced to a few 18th pieces given to the church as gifts during the 19th century. Some of this is due to the fact 42oz of St Mary's substantial medieval plate was taken for the King in 1553 leaving only 14oz for the parish. Also removed from the church in the past was an early 13th century oak parish chest, now held by the V&A and a copy of an early type of clock commissioned from a Marlborough clockmaker in 1767.
Great Bedwyn has had several churchmen of note including Thomas Beckington (1390-1465) who was rector of the parish before becoming both secretary to King Henry VI and Bishop of Bath and Wells in 1443 and historian Revd. John Ward (born 1795) who was vicar from 1826-1850 and wrote a history of the parish as well as conducting excavations at the Roman villa site in Bedwyn Brail and carrying out some of the 19th modifications to the church. Both these excavations and further restoration of the church in 1853-5, according to designs by T.H Wyatt, were continued by the succeeding vicar, Revd. William Collings Lukis. An extensive vicarage house was built 1878-9 but sold in 1968 and is now known as Glebe House. The current vicarage is a modern house built in the surrounding land of the old vicarage in 1966.
Church registers, other than those in current use, are held in the Wiltshire & Swindon History Centre from 1538 for burials, 1540 for marriages and 1554 for christenings. They feature the following omissions: burials and baptisms from 1635-6, and burials again from 1769-79.