Most features of the church date from 1858 or from the 1867 restoration by Butterfield, but it has a 14thc. S aisle (c.1320) and W tower (c.1380), and a S porch of 1500. Late 12thc. sculpture is found on the incomplete, re-set N doorway and on the font.

The Domesday Survey does not mention a church at Flitwick, but records that William Lovett held land there. VCH notes that Flitwick was passed to the Countess of Albemarle and that in 1195 it was held by William Earl of Albemarle (VCH, 285). The advowson of the church was given to Dunstable Priory before the reign of Richard I by Philip of Sanville (VCH, 288).

The N doorway was originally set into the N wall of an aisleless nave.

An etching by Fisher, dated 1 May 1813, shows the doorway with 21 voussoirs rather than the 17 now in existence. The additional voussoirs, on the bottom L (2) and R (2) of the arch, are carved with chevron, outlined with a sunken band of beading.

Voussoir 4., according to Fisher's etching, had a beakhead with a strap across the beak, with small human features superimposed on the beakhead form; voussoir 8 had a large human head; voussoir 9 was as voussoir 4; voussoir 12 had a human head with a pointed beard and a small round human head in place of its mouth; voussoir 13 had a human head. All of the above are now barely readable.

Fisher's etching shows the label to consist of 9 stones; stones 3 and 6 are very weathered and not readable.