The Diocese of Hearst–Moosonee is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Ontario. The diocese was erected on 3 December 2018 through the unification of the Diocese of Hearst and the Diocese of Moosonee. The Diocese of Hearst evolved from the Prefecture Apostolic of Northern Ontario erected on 18 April 1919. The Diocese of Hearst–Moonosee is a suffragan diocese in the ecclesiastical province of the metropolitan Archdiocese of Ottawa-Cornwall.

The Archdiocese of Ottawa–Cornwall is a Catholic archdiocese that includes part of the Province of Ontario and includes the suffragan dioceses of Hearst, Pembroke, and Timmins. On 6 May 2020, Pope Francis amalgamated the Archdiocese of Ottawa and the Diocese of Alexandria-Cornwall to create the Archdiocese of Ottawa–Cornwall.