Although there is no structural evidence of a Saxon church, the first firm evidence of a church in Grays is 1040, when a priest, Wulfstan the Wild One, inherited the Manor of Thurrock. The earliest architectural style identified in the present structure and in old drawings is Norman, and it has been concluded that the oldest part of the present building dates from a few years either side of 1100, and consists of the present chancel and part of the nave built by the Peverels, who were then Lords of the Manor.
Sometime between 1152 and 1159, the church was given to the Knights Hospitallers of St John of Jerusalem by William de Ferrers. He had come into possession of the Church and Manor by marrying Margaret the daughter of William Peverel and grand-daughter of the first Norman Lord of the Manor. William de Ferrers not only gave away the Church "for the safety of my soul, and for that of my wife, and for those of my predecessors and heirs" but also sold the Manor at about the same time to Isaac, son of Josce the Rabbi, showing concern for both his spiritual and earthly needs. The manor came into the hands of the King probably on Isaac's death as a method of collecting death duties from those who were not the King's subjects. Their lands were confiscated and then sold back to the heir at a substantial discount. It was Isaac's son who sold the Thurrock manor to Henry de Grey in 1194. Thus started the long association of the de Grey family with the area, which was to give its name to Grays Thurrock.
The south chapel (now the organ chamber) is entered through an arch which is dated to 1280-90, and some authorities date the chapel's construction to that time. However. at least two 19th century drawings show early Norman round-headed windows in its east and west walls, and it is more likely that the arch was introduced in order to improve access to the chapel, and that the chapel dates from the original construction of the church, or even before, for it was a manorial chapel. The tower was added at about 1230.