The town of Ramsey is situated on what was originally an island surrounded by Bury Fen on the south and Stocking Fen on the north, and was approached by a causeway on one side only. The abbey stood on the highest part of the island. The foundation of the abbey is attributed to Ailwine in 969, and the first mention of its leugata or banlieu (the privileged area around the abbey itself) is in a charter of Henry I of c. 1100-02. Until the end of the 12thc., the town was quite unimportant; it is not mentioned in the Domesday survey of 1086. By the end of the 12thc. it had grown enough for the Abbot of Ramsey to obtain the grant of a weekly market. There is no precise foundation date for the church described above, but the hospitium which became St Thomas a Becket's must have been founded c.1180 and seems to have been dissolved before 1291, when the first reference to a parish church occurs. Before this date the parishioners had the right of worship in the abbey church. The dedication at this time (or possibly in 1237, when many churches in the diocese were consecrated under papal pressure) was not to Becket, but (according to Cole) to SS Mary and Benedict.
The nave originally had eight bays. In 1537 the last Abbot of Ramsey, John Lawrence, ordered the executors of his will to make a payment towards the building of 'a Stepule in the Parish Church of Ramsey', but the result of his generosity seems only to have been the construction of a wooden belfry. This fell down in 1672, and the churchwardens then built a new tower with stone from the abbey. It has been suggested that one of the abbey towers was used for the purpose. The present tower arch was presumably constructed at that time, re-using responds from the curtailed nave arcade. Whether the W tower doorway is the original W doorway of the hospitium or an import from the abbey or elsewhere is a matter of conjecture. Stylistically it has no connection with other sculpture in St Thomas's.