A church on the site of St Mary's dates back to the 13th-century, when a Chantry chapel was first recorded there in 1299.

Furthermore, it was considered that Melcombe Regis was "subject to the incursion of foreign enemies, who might surprise the town during Divine service, and depart before the inhabitants could repair home to make resistance".

[1] By the early 19th-century, the church had become too small to adequately serve the population of Melcombe Regis, and had fallen into a dangerous and dilapidated state.

Plans for a church capable of accommodating upwards of 2,000 people were drawn up by James Hamilton of Weymouth, with many seats being free and unappropriated for the benefit of the poor and visitors to the seaside resort.

[6] In June 1815, an Act of Parliament was obtained for the rebuilding of the church and tenders from builders were sought that month.