Purley was previously a rural village but is now a suburb of Reading, despite being situated outside Reading UA. Ribbon development along the Oxford Road, and the building of large housing estates to the south of it entirely subsumed the old village. Most of the old church is gone too, replaced by G E Street in 1870 (but incorporating older fabric). St Mary's has a brick W tower of 1626, a nave with 20thc. N aisle extending along the N side of the tower, and a square chancel with a pointed chancel arch. The 12thc. chancel arch has been reset on the N side of the chancel and is described below. There is also a 12thc. carved font.

In 1086 there were two holdings in Purley. The larger (Purley Magna), assessed at 4 hides, was held by Roger, son of Siefried, and had been held by Beorhtweard before the Conquest. Another, of half a hide, was held by Theodric the Goldsmith in 1086. No church was mentioned in either holding. The overlordship of Purley Magna passed to the honour of Wallingford, and the tenancy to the Huscarle family before the end of the 12thc, remaining in that line at least until the mid-14thc. Theodric's manor of Purley Parva apparently passed to Robert de Sifrewast early in the 12thc, remaining in that family at least until 1302.

The fonts at Spital (Windsor), Tidmarsh and Sutton Courtenay also have intersecting arcading but none is similar to Purley's or as elaborately carved.