We live in a condo owned by one partner — should we have a cohabitation agreement in Ontario?

Yes, this is exactly the situation where a cohabitation agreement is most useful. When one common-law partner owns the home and the other does not, the non-owning partner has no automatic legal right to stay in or receive a share of the home if the relationship ends — unlike a married spouse, who has special rights to the matrimonial home.

Without an agreement, the non-owning partner could still potentially bring a trust claim if they contributed to the condo's mortgage, value, or upkeep. But that is uncertain, costly, and depends on the evidence they can gather. An agreement removes the uncertainty by either confirming the condo is the owning partner's sole property (so the non-owner knows exactly where they stand) or by granting the non-owner a defined interest in the condo in return for their contributions.

The agreement should also address practical matters like what happens if the owning partner wants to sell and the non-owner has no alternative housing, how household expenses and condo fees are divided, and what notice or compensation the non-owner receives if the arrangement ends. If the non-owner is helping pay the mortgage, ensure it is clear in the agreement whether those payments are rent, a loan, or a contribution toward an ownership interest.