PowdAir will fly from at least five airports in the UK as well as Brussels and Rotterdam, the airport's director Aline Bovier told news agency ATS.
Flights will operate five days a week during the winter ski season, with tickets going on sale later this month, according to the operator's website.
Speaking to a UK ski website in February a spokesperson for the airline said the UK airports involved were Southend, Southampton, Bournemouth, Bristol, Manchester and Edinburgh.
The flights will significantly reduce skiers' travel time to major ski resorts in the Valais including Verbier, Crans-Montana, Nendaz, Zinal and Zermatt, all several hours journey from Geneva or Zurich airports.
Flights have already gone on sale through tour operators and the response has been very promising, said Bovier.
The new flight connections could bring “several thousand people a month” to Sion, she added.
They could also prove useful should Sion be successful in its likely bid for the 2026 winter Olympics.
In February national carrier Swiss International Air Lines trialled a flight connection between Sion and London Heathrow, with one flight weekly on a Saturday.
The airline has not yet said whether this will become a permanent operation, however Bovier confirmed that the trial flights were “almost full”.
The airport is also planning to start flights to Portugal through PowdAir or another company in 2018, she said.