The earliest surviving parts of the Church of the Blessed Virgin Mary are the Norman font and the ground stage of the west tower, which was built around 1200.

By 1741 the medieval building was in ruins, and in 1743/44 all but the thirteenth-century bell tower was rebuilt by Norreys Bertie, Lord of the Manor. The Bertie family lived in Weston Manor, which is now a hotel.

The replacement is a characteristically box-like Georgian church, with what were originally plain round-arched windows on the north and south sides. The Georgian building had an ornate plaster ceiling, but this collapsed in 1810. The surviving ornate Georgian surroundings of the south door are of a very high quality.

There is no east window. Instead the blank east wall is dominated by an altarpiece of the Ten Commandments attributed to the Italian master Pompeo Batoni (1708–87), although this has not been substantiated. Weston-on-the-Green is not the only Oxfordshire parish church thought to have a painting by Batoni. The parish church of St Peter in Marsh Baldon, twelve miles south of Weston-on-the-Green, has a Batoni painting of the Annunciation. The other unusual feature within the church is a large wrought iron cross hanging on the north wall above the pulpit, said to have been made by Napoleonic prisoners of war from material rescued from the Spanish Armada.

In the 1870s the building was restored by the architect, R Phené Spiers, with repairs to the tower and the addition of the south porch and new seating. A plan to rebuild the east end with an apse ‘to make the building more churchlike’ was not executed. In 1885 Spiers added a heavy tracery to the Georgian windows and the organ was installed.

The tower used to have three bells, one each cast in the fifteenth, sixteenth, and seventeenth centuries. They were replaced in 1870 with a ring of five, now six, all of which were cast by Mears and Stainbank of the Whitechapel Bell Foundry. There is also a Sanctus bell cast in 1834 by W & J Taylor, presumably at their Oxford foundry.

St Mary’s is a Grade 2* listed building