The hotel was sold in January to Solterra, a Delta developer that will take possession of the East Hastings building this fall.
Since then musicians, activists and community members have gathered more than 20,000 signatures on a "Save the Waldorf" petition.
But although the level C designation will give the historic building some protection, it does not guarantee the property won't be redeveloped.
City Councillor George Affleck said the future of the building is still in the new owner's hands.
"There's not a lot of protection [for the building] but it does put some limitation in the possibility of developing it," he said.
"But mostly it's up to the developer to work with the City and hopefully save the building."
Solterra's CEO Gerry Nichele released a statement saying the company had no intention of demolishing the hotel, which has become a trendy hangout in Vancouver’s arts and culture scene in recent years.
Sandy Garossino, spokeswoman for the Vancouver Loves the Waldorf group, said a heritage designation would become a barrier to demolishing the building, whatever Solterra's future plans are.
"The only way a brand new city like Vancouver can acquire history and character is to preserve what we've got. Otherwise, we'll just be a never-ending train of the latest passing fad," she said.
Solterra says it has no objection to the hotel being added to Vancouver's heritage register.