Before the year 904 there was a Saxon monastery at Plympton, a college of priests who would go into the countryside to hold services even before churches were built. This monastery gave place to an Augustinian Priory in 1121, with a Prior and eighteen monks. The Priory was completely destroyed in 1539, at the time of the dissolution of the monasteries. The church of Plympton St. Maurice was apparently a chapel served by the monks of the Priory, but by 1300 it had become a parish church and had changed its dedication to St. Thomas of Canterbury (Thomas `a Becket), martyred in 1170. Its original dedication must have been to St. Maurice, commander of a Roman Legion (the Theban) who was martyred about the year 290 for refusing to sacrifice to the gods. In 1538 the dedication reverted to St. Maurice, though the church was sometimes known as St. Thomas and St. Maurice. The seven churches under the control of the Priory were in 1547 transferred to the Dean and Canons of Windsor, the present patrons.
Little remains of that Early English church. In the 14th and 15th centuries it was reconstructed in the Perpendicular style of the period; the most notable features of the new church were a tall tower on the old foundations, and the chapel of St. Maurice, the gift of John Brackley, one of the members of Parliament for the Borough in 1382. Various alterations were made over the years; the gallery was removed in 1869, and during the incumbency of the Revd. H.T. Hole, who was Rector for 44 years (1877 - 1921), a complete restoration of the Church was carried out.

In the churchyard near the south porch is a stone cross. The shaft of this cross was found when alterations were being made to the Guildhall in 1861; its approximate date is 1380. It was restored and placed in its present position in 1900.