Sister Bernadette Poirier, one of the 135 Grey Nuns who moved to Square Angus, a new apartment building, last week, said the dwindling number of nuns is a key reason for the move.
The group was unable to remain in the large building which formerly housed more than 1,000 nuns.
"We were all — and we still are — very sad that we had to sell the motherhouse, because we've been there since 1871," she said.
Concordia University bought the property for $18 million in 2004.
Chris Mota, spokeswoman for the university, said the school will continue to welcome the Sisters of Charity.
"For the nuns, this was their life. This was home. This was their family. This was where they worked, where they lived and there's a real connection here and they will always be welcomed back here," she said.
Once the university completes its takeover, the chapel will be converted into a study hall and the nuns' rooms will make way for students.
Concordia University's website also mentions the possibility of housing the faculty of fine arts in the old stone building.
The basement crypt, which holds 276 bodies, will remain on the property..
Mota said the crypt will still be visible to the public but will not be able to enter it.
Though the Quebec congregation has not recruited any new members since before 2000, Sister Bernadette said the nuns' legacy will live on in other ways.
"Religious life will remain. but it will come in another form, not the form that I lived," she said.