Do I need a cohabitation agreement or a marriage contract?

The Family Law Act treats the two the same way, under different names. A cohabitation agreement is for two people who are living together or plan to and aren't married to each other; a marriage contract is for two people who are married or plan to marry. Both can set out how you'll handle property and support, during the relationship or if it ends.

If you sign a cohabitation agreement and later marry each other, the Act automatically treats it as a marriage contract from that point — you don't need to sign anything new for it to keep applying, though many couples update the terms anyway once they marry.

You can use a domestic contract to agree how property will be divided, whether either of you will pay support and how much, and who directs a child's education, religious upbringing or moral training. What you can't do is sign away a court's ability to decide decision-making responsibility or parenting time for a child — those are always decided in the child's best interests at the time, not locked in years earlier.

A marriage contract also can't take away either spouse's rights to the matrimonial home under the Act — those protections apply regardless of what the contract says.

Ontario law doesn't force you to get a lawyer before signing a domestic contract, but it matters later if the agreement is ever challenged. A court looking at whether to uphold the contract asks, among other things, whether each of you understood what you were signing and whether you knew the other's real financial picture at the time.

In practice, that means each partner getting their own lawyer — not sharing one — and giving full, honest disclosure of income, assets and debts before signing, with both documented. Skipping either step is one of the most common reasons a domestic contract gets challenged later.

A court can set aside all or part of a domestic contract if one of you didn't disclose significant assets, debts or other liabilities that existed when you signed it, if you didn't understand what the contract actually meant, or on ordinary contract grounds like duress or unconscionability. Terms trying to make support conditional on remaining “chaste” are automatically unenforceable.

Terms about a child are treated more loosely again, but the test differs depending on what the term deals with. For a term about a child's education, moral training, decision-making responsibility or parenting time, a court can disregard it if doing so is in that child's best interests. For a child support term, the test is different: a court can disregard it only if the term is unreasonable having regard to the Child Support Guidelines, alongside any other support-related provision in the contract — not a best-interests test.

A domestic contract isn't locked in forever. It must be in writing, signed by both of you and witnessed to be enforceable in the first place — and the same rule applies to any later change: an informal understanding to update it doesn't count until it's written down and signed the same way.

Circumstances that often prompt an update include buying a home together, a child being born, a big change in income, or an inheritance one of you receives — revisiting the contract when life changes is usually cheaper and calmer than leaving it to be argued about later.