As Cossio, it was capital of the ancient tribe of the Vasates, and under the Romans one of the twelve cities of Novempopulania,[3] when it was known as Civitas Vasatica[4] In later times it was capital of the district of Bazadais, and was the seat of the bishop of the diocese of Bazas from at least the beginning of the 6th century until 1790.

According to Gregory of Tours, Bazas had a bishop at the time of the Vandal invasion in the 5th century.

[5] The dedication of the cathedral to St. John the Baptist is explained in an account given by the same historian that a lady of Bazas, whom certain hagiographers of the 19th century believe to have been St. Veronica, brought from Palestine a relic of St. John the Baptist at the time of that saint's death.

The town has a Gothic cathedral dating from the 13th to the 16th centuries, now part of the Unesco World Heritage Sites of the Routes of Santiago de Compostela in France.

The N524 forms part of the Itinéraire à Grand Gabarit, a route which has been modified to allow its use by the oversize road convoys conveying body sections and wings of the Airbus A380 airliner, and several upgrades were made to the road through Bazas to this end.