[4] St Giles' Church was founded in 1092 by an endowment from Hugolina de Gernon, the wife of Picot of Cambridge, baron of Bourn and county sheriff.

[5] According to the 12th-century writings of Alfred of Beverley, Hugolina, who had been suffering from a long illness which the king's physician and other doctors had been unable to treat, had prayed to Saint Giles on her death bed promising to build a church in his honour if she were to recover, which she duly did.

Picot reportedly constituted the church, after consulting with the Archbishop of Canterbury, Anselm, and the Bishop of Lincoln, Remigius de Fécamp, under the supervision of the Canon of Huntingdon and his own patronage against the curtain walls of his home at Cambridge Castle.

[6][7] Former county archaeologist Alison Taylor, however, speculates that, rather than founding a new priory, Picot placed an existing minster serving the area in control of the Norman Canons Regular, and that this was done for purely economic reasons.

[7][8] The church was initially served by a group of six Augustinian canons, who remained at St Giles' for twenty years until after the death of Picot, when they were granted land in Chesterton by Pain Peverel upon which they established Barnwell Priory.

The small St Giles' Church continued to operate over the following centuries but failed to develop due to its impoverished location outside the town walls in a densely inhabited area that was badly affected by the Black Death.

[10] The original structure of the medieval church became almost entirely obscured or pulled down by a large post-Reformation extension and the addition of box pews.