What happens if my co-owner stops paying their share of the mortgage in Ontario?

If both of you are on the mortgage, the lender can hold either of you fully responsible for the entire debt, regardless of your private arrangement about who pays what. A co-owner's failure to contribute does not reduce your obligation to the bank. If payments fall behind, the lender can initiate power of sale or foreclosure proceedings against the property, which would affect both owners.

From a co-owner perspective, if you cover the shortfall to protect the property, you may have a legal claim against the non-paying co-owner for the amounts you covered. This is called a claim for contribution. However, recovering those amounts in practice often requires litigation, which is costly and uncertain.

This is exactly the scenario a well-drafted co-ownership agreement is designed to address. It can include provisions that treat a co-owner's failure to pay as a default triggering a mandatory buyout, allowing the paying co-owner to purchase the defaulting party's interest at a formula price.

If you are already in this situation without an agreement, your practical options are negotiation, a court application for partition and sale, or commencing a claim for contribution. Speaking with a real estate litigation lawyer quickly helps you understand which path fits your situation.