Ontario has one family of contracts for couples and the right one depends entirely on where you are in the relationship. Get the category right, meet three formalities, and disclose everything. Most contracts that fail in court fail on the third.
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The <a href="https://www.ontario.ca/laws/statute/90f03">Family Law Act</a> groups these agreements together as domestic contracts. A marriage contract is signed before or during a marriage. A cohabitation agreement is signed before or during cohabitation without marriage. A separation agreement is signed after the relationship ends. A paternity agreement deals with support and expenses between unmarried parents. The label follows your timing, not your preference.
A cohabitation agreement does not expire when you marry. It converts: the Family Law Act deems a cohabitation agreement to be a marriage contract if the parties marry each other, and there is no opt-out from that deeming. That is useful, but it also means terms you drafted for a two-year cohabitation will govern a twenty-year marriage unless you revisit them. Read the old agreement before the wedding, not after the separation.
Marriage contracts and cohabitation agreements are forward-looking: what stays separate, how a jointly bought home is held, what happens to a business or an inheritance, whether spousal support is limited or released. Separation agreements are backward-looking and settle what has already happened: equalization, support, parenting, the house. The drafting problems are completely different, and so are the risks.
There are limits on what any of them can do. A marriage contract cannot take away a spouse's right to possession of the matrimonial home. Terms about parenting and about child support are not immune from review — the court applies the child's best interests and the child support guidelines regardless of what the adults agreed. Assume anything touching children is provisional.
The formalities are short and absolute: a domestic contract, and any agreement amending or rescinding one, is unenforceable unless it is in writing, signed by the parties, and witnessed. A kitchen-table agreement typed into an email thread and never signed is not a domestic contract. Neither is a signed document with no witness, however clearly it records what both of you meant.
The same rule applies to changes. Couples who vary support informally for a year, then fall out, discover the variation was never enforceable and the original terms still stand. If your circumstances change, amend the contract properly — in writing, signed, witnessed — rather than by conduct or by a run of payments neither of you documented. Our article on <a href="/articles/amending-a-domestic-contract-after-signing-ontario">amending a domestic contract</a> sets out how.
Independent legal advice is not, strictly, a formal requirement for a domestic contract. It is still the single most useful thing you can do to make one survive. A certificate of independent legal advice on the face of the agreement makes it far harder for the other party to argue later that they did not understand the nature or consequences of what they signed.
Do not share a lawyer. One lawyer cannot advise both parties on an agreement that divides value between them, and an agreement drafted by one party's lawyer and signed by the other without advice is the classic profile of a contract that gets attacked. Our note on the <a href="/articles/diy-domestic-contract-risks-ontario">risks of a do-it-yourself contract</a> covers what usually goes wrong.
A court can set aside a domestic contract, or a term of it, on three grounds: a party failed to disclose significant assets, debts or other liabilities that existed when the contract was made; a party did not understand the nature or consequences of the contract; or the contract fails under ordinary contract law, which brings in duress, undue influence and unconscionability.
The first ground does the most work. Disclosure means real numbers with real dates — account balances, a business valuation, the pension, the debts — exchanged in writing before signing and attached to the agreement. Understating a company or omitting a property is not a technical foul; it is the most reliable way to lose the entire agreement years later. Our article on <a href="/articles/financial-disclosure-setting-aside-domestic-contract-ontario">disclosure and set-aside</a> goes deeper.
The second ground is about process. Signing on the eve of a wedding, without advice, in a language you do not read well, or under pressure of a threat to call things off, all feed the argument that you did not understand what you were giving up. Build the timeline deliberately: draft early, exchange disclosure, give the other party time and their own lawyer.
Treadstone drafts and reviews all four kinds of domestic contract, and provides the independent legal advice certificate when the agreement was drafted by the other side's lawyer. Family work is quoted as published flat fees — the uncontested divorce, for reference, is $1,693.87 with taxes included — and confirmed in writing before the file opens. See the <a href="/pricing">pricing page</a>, our <a href="/articles/formal-requirements-valid-domestic-contract-ontario">formal requirements guide</a>, and the rest of our <a href="/family">family law practice</a>.
None, in Ontario. "Prenup" is imported vocabulary; the Family Law Act calls it a marriage contract, and it can be signed before or during the marriage. The same formalities, disclosure obligations and set-aside grounds apply either way. What changes with timing is bargaining position, not legal category.
It matters more, not less. Unmarried partners are not entitled to equalization of net family property, so the default outcome can be harsh for whoever did not hold title. A cohabitation agreement lets you decide how a home, a business or contributions of unpaid work are treated, rather than leaving it to a trust claim years later.
Yes. A domestic contract, and any agreement amending or rescinding one, is unenforceable unless made in writing, signed by the parties and witnessed. The witness requirement is not decorative — agreements have failed on it alone. Keep the signed original with the witness signatures, not just a scan of the signature page.
It depends which contract. A separation agreement can deal with decision-making responsibility and parenting time; a marriage contract or cohabitation agreement cannot — the Family Law Act limits those to the right to direct a child's education and moral training. Wherever children are dealt with, the terms are reviewable: a court applies the child's best interests to parenting and the guidelines to child support, regardless of what the adults agreed. Treat the children's provisions as a plan the court may adjust, and the financial provisions between the adults as the binding part.
Yes, but only the same way you made it: in writing, signed and witnessed. Informal variations by conduct, text message or handshake are unenforceable, and people discover this at exactly the wrong moment. If income, health or living arrangements have changed materially, amend the contract formally or replace it.
Open your file tonight — a licensed Ontario lawyer will confirm everything with you by tomorrow.