Built on a cruciform plan, this modified Gothic Revival church has prominent, uneven bell towers topped by steep polygonal spires. Red brick is accented by limestone ornament, which also frames the facade's large rose window and towers flanking a gabled parapet above a statue of St. Mary in a niche. Inset windows beneath the bell towers were once entrance doors, closed off by the 1968 addition of a contemporary entrance ramp and stairway, which provide a meditation area between church and street. The center landing of this new entrance features a bronze railing by Edgar Britton, a prominent Colorado sculptor. As was the case with many other financially struggling Catholic parishes, the basement (1891) was used as a church while fund raising for a more formal church dragged on. The superstructure of St. Mary's was not completed until 1898, and the bell towers were not added until 1903.