The church of St. Mary’s is first mentioned in 1100 when it was passed to the Gloucester Abbey of St Peter’s by Harold of Ewias. He was the son of Ralph, Earl of Hereford, who had acquired it from Alfred of Marlborough after 1086. By 1280 the church was granted back to John Tregoze in exchange for the church of Burnham. It would be the lords of Tregoze, later St. John, who would exercise patronage rights for St. Mary’s.
The 13th century origins of the church were established due to the village settlement of what was then just called Lydiard. There is evidence of a track, disused since 1964, believed to be the main village street leading to the Church. Parts of the Church date back to these 13th century origins, in particular the nave, parts of the north aisle and the font. However the 15th century saw it refurbished with a new roof, tower and many other aspects, including the commission of many wall paintings.
The brilliant furnishings within St. Mary’s, and the many monuments adorning the Church, are owed to the St. John family of Lydiard Mansion treating the Church as a family chapel.
The 17th century saw Oliver St. John and his wife Margaret Beauchamp richly furnishing St. Mary’s. A painted triptych was established in 1615, and the outer panels show a genealogical table boasting family connections with many important people. In 1633 the St. John’s gave the ‘S’ shaped chapel classical columns, which carried a straight entablature, whilst the next year saw the remodelling of the St. John’s tomb by Sir John St. John. The finest effigy is that of Sir John St. John himself, due to the fine detail put into his features and hands. Carved in 1634, fourteen years before his death, it depicts Sir John, his two wives and their many children.
This period also saw the refurbishing of the glass window within St. Mary’s, although some of the 15th century glass still remains. St. John is responsible for the east window of the chancel, which depicts an olive tree and the figures of the two St. Johns, as an allusion to Oliver St. John, Viscount Grandison.
St. John was also responsible for the first three bells at the church, dated 1635, which increased to five by 1670. The fourth bell was recast by Abraham Rudhall in 1757 whilst the fifth was done earlier by William and Robert Cor in 1701.
The west tower held Somerset tracery in the bell openings, whilst there was a pretty sanctus-bell turret at the east end of the nave. The only memorable piece after the 17th century is known as the Rysbrack monument. Named after its creator, it depicts the 2nd Viscount St. John and stands at the south end of the chapel.
There is little known about the rectors of Lydiard Tregoze. However it is understood that two rectors, Walter Elyot, 1445, and Alexander Thornton 1576, were deprived of their living, however it is not known why this was so.
By 1839 the rectory ‘rights of presentation’ had been sold, placing Giles Debauchey as rector; this rather than the St. John’s wish to have a beloved cousin take the position, as the decision now no longer rested with them. During the Victorian era, Debauchey oversaw repairs on St. Mary’s, which included a new pulpit to replace the one previously facing the St. John family pew, which had first come into the church in the 17th Century.
During the 19th Century the church saw a fifty year period of little or no rent payments which in turn meant that repairs were limited. Small growth in profit which came from new rent fixing went towards the upkeep of monuments and in 1964 the income of fifty pounds was spent on insuring these pieces.