Leuk is home to one of the known installations of Onyx, the Swiss interception system for signals intelligence gathering.

Scattered La Tène era graves with poppy-head pins, brooches and a belt hook have been found in Leuk.

In the 6th century it belonged to the demesne of the King of Burgundy Sigismund, who donated it to the Abbey of Saint-Maurice.

The local population of Romanized Celts gradually became Germanized around the turn of the millennium due to invading Alamanni.

It was richly furnished with altars and sculptures and was consecrated in 1494 as St. Stephan's Church by Bishop Jost von Silenen.

In the charnel house, with its dance of death fresco, 26 statues dating from the 13th to 16th centuries were discovered in 1982 under about a meter (three feet) of bones.

A Marian shrine, whose hermitage was inhabited by a hermit around 1720–1885, is one of the most important baroque rooms of the Valais.

[5] In the Early and High Middle Ages Leuk changed owners repeatedly until 1138 when it finally came under the authority of the Bishop of Sion.

In 1285 they built a hospital and in 1310 they added a warehouse, one on the old trade route between northern Italy and the markets of Champagne.

With the warehouse they established a group of teamsters that provided extra draft animals to help wagons make it over the mountains.

In the 14th century the castle ruled over three surrounding areas; Loye (Lobio), Tschablen (Cabulo) and Galdinen (Caldana).

The two gorges and the river Rhone to the south provided excellent natural fortifications for the growing town.

The first was the victory in 1296 of troops loyal to the bishop over the upper Valais nobility (including the vom Turn and von Raron families), who were supported by nobles from the Bernese Oberland.

In 1386, Leuk prevented the advance of Count Amadeus VII of Savoy into the Upper Valais with the destruction of Dala bridge.

In 1541, Ulrich Ruffiner built the present Gothic-style town hall on the ruins of the Viztumsturm.

[5] In the Middle Ages, the local economy was based on the transport of goods, alpine herding, farming and viticulture.

The town produced gravel from the banks of the Rhone in the Pfynwald (Pfyn forest), until this was restricted for environmental reasons in the 1970s.

In 1908 the Alusuisse-Werke (now Alcan Ltd) opened a processing plant in Chippis and Steg which provided jobs for many people from Leuk.

In 2005, the train station in Susten was rebuilt with a new railway bridge over the Rhone and a new rail tunnel towards Salgesch.

At the beginning of the 21st century, it is also the educational, legal and services center in part due to the satellite earth station of International Teleport Switzerland AG.

The large antennas of the earth station have made Leuk into a major intercontinental telecommunications center.

[5] Near the earth station are the antennas of the Swiss military Onyx system for electronic intelligence gathering.

As part of the restoration, one of the medieval towers was topped with a glass cupola by the architect Mario Botta.

[6] The historical population is given in the following chart:[5][14] The Dalaturm, the Church of St. Stephan, the Rathaus (Town council house), the Ringacker Chapel of Mariä Empfängnis with the Hermitage and Zen-Ruffinen Castle are listed as Swiss heritage site of national significance.

The entire small town of Leuk and village of Erschmatt are part of the Inventory of Swiss Heritage Sites.

In the tertiary sector; 91 or 13.7% were in wholesale or retail sales or the repair of motor vehicles, 48 or 7.2% were in the movement and storage of goods, 95 or 14.3% were in a hotel or restaurant, 18 or 2.7% were in the information industry, 28 or 4.2% were the insurance or financial industry, 42 or 6.3% were technical professionals or scientists, 83 or 12.5% were in education and 204 or 30.8% were in health care.

The education system in the Canton of Valais allows young children to attend one year of non-obligatory Kindergarten.