What Makes a Domestic Contract Enforceable in Ontario?

You and your partner have agreed on how to handle your finances, property, and future — and you want it in writing. But a domestic contract that isn't properly made is worth very little. Ontario's Family Law Act sets out clear requirements, and courts have a track record of setting aside agreements that were improperly signed, negotiated under pressure, or built on incomplete financial information.

Understanding what makes an enforceable domestic contract in Ontario before you sign — not after a relationship breaks down — is the smartest move you can make.

What Is a Domestic Contract?

Under Ontario's Family Law Act, the term domestic contract covers three main agreements:

• Marriage contracts (commonly called prenuptial agreements or prenups) — signed before or during marriage
• Cohabitation agreements — signed by couples living together outside of marriage
• Separation agreements — signed when a relationship ends

Each type has specific rules about what it can and cannot address, but they all share the same core enforceability requirements.

The Four Core Requirements

1. The Agreement Must Be in Writing

An oral domestic contract — no matter how clear the understanding between partners — is not enforceable under the Family Law Act. The agreement must be a written document.

2. Both Parties Must Sign

Both people must sign the document. A one-sided agreement, or one signed only by the person who benefits most from it, has no legal effect.

3. The Signatures Must Be Witnessed

Each party's signature must be witnessed by a separate, independent witness. A party cannot witness the other's signature. Close family members — parents, siblings, adult children — can technically serve as witnesses, but best practice is to use a neutral third party, such as a paralegal, commissioner of oaths, or lawyer.

4. There Must Be Full Financial Disclosure

Both parties must fully and honestly disclose their financial situation — assets, debts, income, and liabilities — before signing. Courts have set aside agreements where one party hid assets, understated income, or simply failed to provide enough information for the other party to make an informed decision.

Why Independent Legal Advice Matters

Independent legal advice (ILA) is not technically a statutory requirement for a domestic contract to exist, but it is arguably the single most important safeguard for enforceability.

Here's why:

• A court asked to set aside an agreement will look closely at whether each party had their own lawyer review it and explain the legal consequences.
• If one party received ILA and the other didn't, the party without advice has a much easier argument that they didn't understand what they were signing.
• A lawyer providing ILA signs a certificate of independent legal advice, which becomes strong evidence that the agreement was entered into voluntarily and with understanding.

Each party needs their own lawyer. Your partner's lawyer cannot also advise you — doing so would be a conflict of interest and would undermine the entire purpose of independent advice.

Grounds for Setting Aside a Domestic Contract

Even a properly signed, witnessed agreement can be challenged. The Family Law Act specifically allows a court to set aside (invalidate) a domestic contract if:

• A party failed to disclose significant assets or debts that existed at the time of signing
• A party did not understand the nature or consequences of the contract
• There was duress, fraud, or undue influence — for example, one party was pressured to sign shortly before a wedding, or the agreement was sprung on them with no time to consult a lawyer
• The terms are unconscionable — meaning they are so extremely unfair to one party that a court won't uphold them

Courts take a contextual approach. The closer the signing to a major life event (the wedding date, the birth of a child, an illness), the more carefully a court will scrutinize whether the process was fair.

Provisions That Courts Will Not Enforce

Even within a properly executed agreement, certain clauses are unenforceable in Ontario:

• Anything that limits a child's right to support — parents cannot contract away a child's entitlement to support; courts will override those clauses
• Agreements that oust the court's jurisdiction over parenting in a way that is not in the child's best interests
• Possession of the matrimonial home — there are specific restrictions on what a marriage contract can say about possession of a matrimonial home where children are involved

For more on what each type of contract can and cannot cover, see our companion articles on marriage contracts and cohabitation agreements.

Practical Steps to Make Your Agreement Stand Up

1. Start early. Don't negotiate and sign the same week as the wedding or move-in date.
2. Exchange sworn financial statements or detailed financial disclosure letters.
3. Each party retains their own lawyer and receives a signed ILA certificate.
4. Read the whole document — every clause — before signing. Ask questions.
5. Keep a copy in a safe place, along with the financial disclosure exchanged.
6. Review the agreement when circumstances change — children, major assets, provincial moves can all shift what's fair and what a court might enforce.

Frequently asked questions