In May the Italian winter sports federation (FISI) had asked to postpone the event by a year due to uncertainties linked to the COVID-19 pandemic and its negative impact on the country.
"It was clear that there was a strong desire to carry out the event in 2021... FISI expressed to the FIS Council the importance of these World Championships to be staged in 2021 as a positive signal for the entire country," FIS said in a statement.
FISI said FIS had decided to provide a financial guarantee of up to 10 million Swiss francs ($11 million) to Italy should there be a new outbreak of novel coronavirus, the federation said in an online statement.
"It is a form of guarantee that the federation wanted to give to Italy, hoping that there is no need and that the World Championship will go ahead regularly," FIS President Gian Franco Kasper was quoted as saying in the FISI statement.
Italy has been one of the worst-hit countries in the world by the COVID-19 pandemic, with almost 34,800 deaths and close to 240,800 cases.
Alessandro Benetton, Cortina 2021 Foundation Chairman, said: "We worked hard in the last few years without even stopping during the toughest months of the coronavirus emergency... the team is ready and we are putting the finishing touches to the infrastructure to host the competitions".
Cortina d'Ampezzo, located in the Dolomites, will also host the 2026 Winter Olympics together with the northern Italian city of Milan.