st marie's is constructed in red brick with sandstone dressings, and has blue brick banding. it is roofed with welsh slate. the plan consists of a single cell. the nave has a polygonal apse at the east end, and there are seven-bay aisles under lean-to roofs at the sides. on the gable at the west end is a bellcote with a cross finial. at the west end are three stepped lancet windows over a double doorway. the bays of the aisles are separated by stepped buttresses, and each bay contains a pair of lancet windows. on the north side of the church is an arched doorway under a gable, the tympanum of the arch containing a mosaic with the inscription "i am the immaculate conception". at the east end of the church the aisles terminate in gables, each gable containing a circular opening and surmounted by a cross finial. each facet of the apse contains a pair of lancet windows.