When the Romans invaded Britain in AD 43 and headed north, they would have found a substantial Iron Age settlement at Ancaster. After first establishing a marching fort, the Romans settled in the town, subsequently building Ermine Street which passed through the settlement to link London to the north. A town grew up beside the road and this was served by a pagan shrine which once occupied the site of the existing St Martins church.

It is not known exactly when the church was established in Ancaster but the attribution to St Martin is often associated with churches on Roman military sites. It would be too much of a leap to suggest this means there was a church on the site in the Roman period as it is quite possible the establishment and naming was a much later event. However the possibility cannot be completely ruled out. It is also to be noted that St Martin was associated with the destruction of pagan shrines and temples and, given that the church stands on the site of a Romano-British shrine, it is possible that this was the reason for the church to be named after him.

According to Nikolaus Pevsner, in his county based gazetteer of the Buildings of England, the earliest parts of the church - the Chancel and the North Arcade - are Norman, dating to between 1160 and 1170 AD. However it is possible there are traces of an earlier Saxon church to be found in amongst the jumble of different styles that characterise Ancaster's oldest standing building.

Reconstruction of the east wall of the church in the 1960s revealed two Roman stone carvings placed in the north east buttress, one of a male head and the other with two possible female heads, as well as traces of a triple 12th century window which was replaced by a new window in the 14th century.

Other notable features on the outside of the church include a possible Sheela Na Gig, an ithyphallic male figure and a possible pair of exhibitionist gargoyles. The Sheela Na Gig Project has more information.