The Diocese of Namur (Latin: Dioecesis Namurcensis) is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Belgium.^[1] It is a suffragan of the Archdiocese of Mechelen-Brussels.^[2] The diocese is a suffragan in the ecclesiastical province in the metropolitan Archdiocese of Mechelen-Brussels. Its cathedra is found within St. Aubin's Cathedral in the episcopal see of Namur.

The diocese was constituted as a suffragan see of the new metropolitan see of Cambrai by the papal bull of 12 May 1559 establishing the new bishoprics in the Low Countries. Its territory had previously belonged to the Diocese of Liège. After suppression in the French period the diocese was re-established by the Concordat of 1801, its extent matching that of the Department of Sambre-et-Meuse, and as suffragan of the Archdiocese of Mechelen. On 14 September 1823, the territory of the diocese was extended to include Luxembourg, which had previously been part of the Diocese of Metz. After the Belgian Revolution of 1830, a vicar apostolic was appointed for those parts of Luxembourg under Dutch control. As a result of the Treaty of London (1839) formalising the partition of Luxembourg between the Grand Duchy of Luxembourg and the Belgian Province of Luxembourg, in 1840 ecclesiastical jurisdiction over the whole territory of the grand duchy was given to the vicar apostolic of Luxembourg, its loss to the Diocese of Namur being formalised on 7 October 1842.^[3]

In 1907, the Diocese of Namur numbered 583,722 inhabitants, 36 deaneries, 37 parishes, 677 succursals, 96 auxiliary chapels, 111 curacies paid by the State. Within the diocese, religious congregations administered 2 orphanages for boys, 7 for girls, 1 mixed, 18 hospitals or infirmaries, 4 clinics, 194 infant schools, 1 house of rescue, 6 houses for the care of the sick in their homes, 1 asylum for deaf mutes, 2 houses of retreat, 1 insane asylum.^[3]

St Aubin's Cathedral in Namur was founded as a collegiate church in 1047 by Albert II of Namur. The first dean, Frederick of Lorraine, brother-in-law of Albert II, about 1050 secured from Mainz Cathedral a portion of the head of Saint Albinus, to whose patronage the collegiate church was dedicated. In 1057 Frederick became pope under the name of Stephen IX. In 1209, Pope Innocent III formally took the church under his protection.^[3] With the exception of one tower, the cathedral was entirely rebuilt in Baroque style in the 1750s.

The diocese also houses a minor basilica, the Basilica of Saint Maternus in Walcourt.