The Diocese of Hearst–Moosonee (Latin: Dioecesis Hearstensis) 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.

[1] 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 territory that would form the diocese was elevated to an apostolic vicariate on 17 November 1920.