Several of the bishops united both offices: Wilcharius (764-780), previously Archbishop of Vienne, whence he had been driven by the Moors; St. Alteus, who received from the pope a bull of exemption in favor of the monastery (780); Aimo II, son of Count Humbert I of Savoy, who entertained Leo IX at Saint-Maurice in 1049.

Taking this donation as a basis, the bishops of Sion extended their secular power, and the religious metropolis of the valley became also the political centre.

The attempts of the bishops of Sion to carry their secular power farther down the Rhone were bitterly and successfully opposed by the abbots of Saint-Maurice, who had obtained large possessions in Lower Valais.

Especially in the 14th and 15th centuries, the benefactors in these traditional struggles were often the rich peasant communities of Upper Valais, which were called later the Sieben Zehnden (the "seven tithings"), who exacted increasing political rights as the price of support, beginning with the success of the rebellion of 1415–1420.

In the early 17th century, the Seven Tithings began to mint their own coin, which was vigorously opposed by the bishops until they finally had to cede temporal power to the Republic in 1634.

Linked to the Old Swiss Confederacy since the 15th century, the Valais region was for long divided between the French party (typified by Georg of Supersaxo) and the Burgundian-Milanese alliance, to which a powerful personage, Cardinal Matthaeus Schiner (1465-1522), bishop of Sion, had thrown his support.

In return for his support, Julius II made Schiner a cardinal and in 1513 accepted direct control of the see, which gave the Bishops of Sion much of the authority of an archbishop.

Both Adrian II and his successor Hildebrand Jost (1613-1638) were again involved in disputes with the sieben Zehnten in regard to the exercise of the rights of secular supremacy, which were finally settled in 1630, when the Bishops relinquished their territorial rule.

In 1798 Valais, after a struggle against the supremacy of France, was incorporated into the Helvetic Republic, and Prince-bishop Joseph Anton Blatter (1745-1807) went into exile in Novara.

As partial compensation for the loss of his secular power, the bishop received a post of honour in the Diet of the canton and the right to four votes.