[1] The first Catholic Chapel on the Island to be constructed after the Reformation was built by Father Miles McPharlan who was in situation from 1803 to 1820, on land which was gifted to the church by Lieutenant Colonel John Taubman Goldie-Taubman, Speaker of the House of Keys.

[6] However by the 1850s Douglas was far outstripping Castletown both in population and civic importance, it thereby becoming apparent that a larger church was required which would be situated in the centre of the town.

Gahan was highly industrious in raising the required funds, and the foundation stone of St. Mary's was laid by the Right Reverend Dr. Alexander Goss, Bishop of Liverpool, on 28 October 1857.

[8][9] As part of the late Queen Elizabeth's Platinum Jubilee celebrations in June 2022, Douglas was awarded city status.

[1][5] Today St. Mary's continues to play an active part in the religious and secular life of the local community.