[2] From the Anglo-Saxon era until the Dissolution of the Monasteries St Mary's was the church of a Benedictine priory.

In about 1060 King Edward the Confessor (reigned 1042–66) granted the monastery to the Abbey of St Denis in France,[3] making it an alien priory.

According to the chronicler Matthew Paris (circa 1200–1259), in 1250 Richard, 1st Earl of Cornwall stayed at St Denis and bought Deerhurst Priory from the abbot.

He took over the priory, dispersed the monks and planned to build a castle at Deerhurst on the bank of the River Severn.

King Edward III seized alien priories in England in 1337, so that their incomes went to him instead of their mother houses in France.

In 1389 the priory was let for £200 a year to a Sir John Russell and a chaplain called William Hitchcock.

But King Henry VI seized the priory in 1443, and four years later granted it to the recently founded Eton College in Buckinghamshire.

But Edward revoked the grant in 1467, claiming that Buckland had appointed only one secular chaplain, had withdrawn hospitality and had wasted the revenues of the priory.

[3] The King granted the priory to Tewkesbury Abbey instead, on condition that the abbot maintain a prior and four monks at Deerhurst.

The nave is narrow and tall: an Anglo-Saxon style seen also at Escomb, Jarrow and Monkwearmouth in County Durham.

[7] Next the west porch was raised by the addition of a third storey, and the porticus side chapels were extended westward, parallel with the nave.

On the third floor of the tower, on the east side, is a double triangular-headed opening into the nave with stylised capitals and fluted pilasters with reeded decoration.

Below, at first floor level, is a blocked doorway, sited off-centre, which most likely led to a gallery in the nave.

[4] Around AD 1200 the separate porticus were knocked through and extended westward as north and south aisles, running the length of the nave and partly overlapping the west tower.

For each aisle a fine three-bay Early English arcade with moulded arches was inserted in the nave wall.

[9][10] The twin staircase tower arrangement was included only in the larger Anglo-Saxon churches in England (e.g. possibly Winchester and Canterbury), which have now been lost.

[11] The Regularis Concordia, written about AD 973 as part of the English Benedictine Reform, includes instructions on how bells should be rung for the Mass and holidays.

[12] This is about the time that the height of St Mary's west tower was increased to create the present belfry.

There are similar Anglo-Saxon animal heads in the parish churches of Alkborough in Lincolnshire and Barnack in the Soke of Peterborough.

[4] In the church is a double monumental brass to Sir John Cassey (or Cassy) and his wife (circa 1400).