The Diocese of Bazas, centred on Bazas in Aquitaine, covered the Bazadais region, known under the Romans as the Vasatensis pagus after the ancient occupants, the Vasates. In the 2nd century it was part of the Novempopulania, one of the seventeen provinces of Gaul. The diocese must have been created between the first and the third centuries, but because of the large numbers of invaders that passed through this region - Arians, Saracens, Normans - the list of bishops is much reduced during the first millennium. The first bishop of this diocese is mentioned, without a name, by Gregory of Tours in his De gloria martyrum.
The diocese of Bazas, the seat of which was Bazas Cathedral, was bordered on the north by the diocese of Périgueux, on the east by the diocese of Agen and the diocese of Condom, on the south by the diocese of Aire and the diocese of Dax, and on the west by the archdiocese of Bordeaux. It was divided into three archdeaconries.
It was suppressed during the French Revolution by the Legislative Assembly, under the Civil Constitution of the Clergy (1790). By the Concordat of 1801 its territory was unequally divided between the dioceses of Aire, Agen and Bordeaux. The title of the diocese of Bazas was preserved and assigned to the Archdiocese of Bordeaux-Bazas.