What is the difference between a cohabitation agreement and a marriage contract in Ontario?

Both are types of domestic contracts recognized under the Family Law Act, and they serve a similar purpose — allowing a couple to set their own rules for property and support rather than relying solely on the defaults in family law. The key difference is timing and the relationship status of the parties.

A cohabitation agreement is entered into by partners who are living together or planning to, and who are not married. It typically deals with who owns what property, support arrangements, and financial responsibilities during or after the relationship. A marriage contract (sometimes called a prenuptial or prenup if signed before the wedding, or a postnuptial agreement if signed after) is made by parties who are married or planning to marry.

Ontario's Family Law Act specifically provides that a cohabitation agreement automatically converts into a marriage contract if the parties subsequently marry — so the work done upfront is not wasted. Both types of agreement have the same formal requirements (in writing, signed, witnessed) and the same grounds for being set aside (non-disclosure, duress, lack of understanding).