St. Mary’s began as a sandstone church in 1889, built near the Elbow River on land provided by the Canadian Pacific Railway. The area was called the Mission District, due to the settlement of Father Albert Lacombe in the area in 1884. The original Catholic mission was called Notre-Dame-de-la-Paix. The land was used to establish a French-speaking incorporated village called Rouleauville, which subsequently became overwhelmingly English and was annexed by Calgary in 1907 (making St. Mary's part of Calgary). ...
When the Diocese of Calgary was formed on November 30, 1912 by Pope Pius X, St. Mary’s became the Cathedral as the seat of the Bishop.

Demolition of the sandstone cathedral began on July 21, 1955, and on October 30, 1955 the cornerstone for the Cathedral was laid. Construction was completed in February 1957.... Source: Wikipedia