The Diocese of Tournai is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Belgium. The diocese was formed in 1146, upon the dissolution of the Diocese of Noyon and Tournai, which had existed since the 7th century. It is now suffragan in the ecclesiastical province of the metropolitan Archdiocese of Mechelen–Brussels. The cathedra is found within the Cathedral of Notre-Dame de Tournai, which has been classified both as a major site for Wallonia's heritage since 1936 and as a World Heritage Site since 2000.

The Catholic Church in Belgium, part of the global Catholic Church in Belgium, is under the spiritual leadership of the Pope, the curia in Rome and the Episcopal Conference of Bishops.