The earliest surviving part of the church is the lower part of the crossing tower which is early 12thc. and which has two plain round-headed splayed windows, one on the N and one on the S wall. A S aisle was added in the late 13thc. and the N aisle was rebuilt at this time. A clerestorey was also built at this time. The chancel is 14thc. The nave and aisles were again rebuilt in the 15thc. as was the upper part of the tower. The church underwent major restoration in the 1950s and 60s, and the clerestorey was dismantled at this time. The church was rededicated in 1971. Early 12thc. sculpture is found on the S doorway to the tower.

The Domesday Survey does not mention a church at Thurleigh, but records four landholders: Miles Crispin, Hugh de Beauchamp, Robert d'Oilly and Walter of Flanders.

At the end of the 12thc. the de la Leye family held the advowson and Hugh de la Leye gave it to Canons Ashby Priory (Northamptonshire), founded by his father Stephen in the reign of Henry II (1154-89). Stephen de la Leye was the son of Hugh of Flanders, Walter of Flanders' brother.

An engraving made in 1813 by Thomas Fisher shows the impost of the S doorway to be chamfered, with incised zig-zag along the chamfer. A drawing of 1843 held in the Dryden Collection at Northampton Public Library also shows these details (Hare, 40, note 19.)

Although the proportions of the doorway are Anglo-Saxon in character the tympanum form and the decoration of the imposts and label indicate a post-Conquest date. The carved figures on the tympanum demonstrate Anglo-Saxon influence, in both theme and form. Another tympanum depicting the Fall is found at Caton in Lancashire.

VCH dates the tower to 1130.

Hall and Hutchings record the presence of 12thc. fragments which had been reused in the clerestorey walls and windows. Among these are fragments of shafts, plinths and fragments with 'scallop and stiff leaf motifs' . Photographs of the fragments are included in Hall and Hutchings report, but they do not appear to be Romanesque. There seems to be no record of the current location of the fragments.