Sion fulfilled all the criteria to win the right to host Switzerland's third winter Games after 1928 and 1948, both held in St Moritz, the national Olympic body's executive council said.
The decision will be formally ratified on April 11th by the Sports Parliament, comprising Switzerland's 86 federations and Swiss International Olympic Committee members.
In a February 12th referendum voters in the canton of Graubünden, where St. Moritz and Davos are located, rejected the idea of hosting the Olympics.
It was the second time in five years that residents had rejected such a plan, after a 2013 referendum quashed a proposal for Graubünden to host the 2022 winter Games.
That left the way forward for the only other potential Swiss candidate, a joint bid by the cantons of Valais and Vaud with Sion as the proposed host city.
Under the proposal, Olympic events would be spread throughout 14 towns and cities in the two cantons, including Lausanne, Champéry, Crans-Montana, Verbier and Zermatt.
Sion will have to face off against other potential candidates Calgary in Canada, Sapporo in Japan and Innsbruck, Austria. The IOC will make its choice in 2019.
The 2018 Winter Games will take place in Pyeongchang, South Korea, with Beijing hosting in 2022, the first city to stage both a winter and summer Olympics.