[3] St. Mary's is in the centre of Leigh by the Civic Square, which was originally the market place, next to the library and opposite the town hall.

[4] For several hundred years it was the mother church for the six townships, Westleigh, Pennington, Bedford, Astley, Atherton and Tyldesley, that made up the ancient ecclesiastical parish.

In 1871–73 the church, apart from the tower, was rebuilt by the Lancaster architects Paley and Austin at a cost of £8,738 (equivalent to £980,000 in 2023),[5] providing seating for 710 people.

[7] In 1909–10 the same practice, then known as Austin and Paley, added a choir vestry to the north of the church, and recased the tower.

[9] James Irvine, vicar, was so anti "non-conformist" that he refused burial or blessing of those, including children, that had died and required a final resting place.

[10][a] The church has a six-bay nave and two-bay chancel under a continuous roof with a clerestory and crenellated parapet.

The tower, is also castellated retaining the 16th century studded oak west doors beneath an elliptical arch.

Nikolaus Pevsner describes the six bay interior with octagonal piers as being "impressive in scale".

Pevsner describes the reredos and altar designed by Austin and Paley as "extremely handsome" and "gorgeously painted" in gold, red and green by Shrigley and Hunt.

[2] The Speakman window is of interest as it depicts scenes from the industries on which Leigh was built, panels include weavers, engineers and colliers.

[17] Wooden fittings also saved from the earlier church include an altar table of 1705 by Thomas Naylor in the Lady Chapel and oak canopies from the churchwardens seats of 1686.

[2] Over the nave near the tower is an 18th-century brass chandelier, "a cut above the norm" according to Pevsner, which was retained from the old church and converted to electricity.