Seat of a castle belonging to the Bishop of Sion, it is first mentioned in 1052. From the 12th century, the town was under the control of Savoy, who held it until 1475, turning it into one of the main commercial and military centres of the Valais region.

The origins of the town date back to very ancient times. During the Mesolithic period (around 10,000 – 5,500 BC), hunters may have inhabited the area, although excavations in the first half of the 20th century have not confirmed their presence. In the Neolithic period, the site was already inhabited, as evidenced by the findings of the Bourneaux tomb, dated around 4,000 BC, and other Bronze Age tombs at the foot of the hill, between the Salentze river and the Bourneaux. In addition, the remains of a Roman villa from the 2nd century, found near the Salentze river, indicate that the area was also of great importance during Roman times. In the 6th century, the first Christian sanctuary in Saillon was built. The foundations of the Carolingian church that stood there are still visible, and the choir, reworked over time, forms today’s Chapel of St Lawrence. With the instability that followed the end of Charlemagne’s empire, the population moved to the hill, which was easier to defend. In 1052, Saillon Castle was already a property of Bishop Aymon of Savoy, and its strategic position attracted Savoy, who took possession of it at the beginning of the 13th century. In 1260, Duke Pierre II had the defences reinforced and the Bayart keep built. Under the rule of the Dukes of Savoy, Saillon had the ambition of becoming a commercial centre that would overshadow nearby Sion, under the control of the bishop. However, this ambition vanished in 1475, when the Upper Valais patriots, during a period of instability, conquered the Lower Valais and destroyed the Savoy castles, including that of Saillon, which was burnt down. From then on, the village reverted to being a quiet rural centre, far removed from the military and commercial ambitions of the past.