 The Diocese was established on 22 September 1844, under the name of the Diocese of Arichat, on territory split off from the Diocese of Halifax.Its cathedral (now Église Notre Dame de l’Assomption) was located on Cape Breton Island, in the port town of Arichat.On 23 August 1886, the diocese was renamed the Diocese of Antigonish, and its episcopal see moved to St. Ninian's Cathedral, on the Nova Scotia mainland in the town of Antigonish.