The building's former owner, the University of Montreal, would not confirm the identity of the buyer — only that the former convent had been sold.
According to the City of Montreal's property value database, the building is worth more than $31 million.
Several years ago, the university blocked the building's sale to a condo developer. With a sale now confirmed, some people are wondering what the unknown buyer's intentions are for the 25,000-square-metre property, which flanks the north side of Mount Royal.
Projet Montréal leader Luc Ferrandez has been fighting for the building to maintain an institutional role since rumours began swirling about its sale last summer.
The Outremont building, built in 1925 by a congregation with other properties in and around Montreal, has stood vacant at 1420 Mount-Royal Avenue for years.
A condition of its sale is that it must respect the area's residential zoning rules.
University of Montreal said the building costs about $1 million a year in heating and maintenance, and it would need at least $140 million in renovations to bring it up to code.
Though it asked for assistance, the university was unable to persuade the provincial government to help it renovate the building.