For many couples in Ontario, a marriage contract offers peace of mind. Whether you’re entering your first marriage, remarrying, or simply planning for the future, a well-drafted contract can help define how assets, property, debt, and spousal support will be handled during your relationship, and if it ends.
But what happens if things change — or go wrong?
Can you challenge a marriage contract in Ontario? Can a marriage contract be overturned? What makes a marriage contract invalid?
In this post, we break down what a marriage contract is, how legally binding it really is, the grounds for challenging one in Ontario, and what to do if you’re concerned about the validity of your own agreement.
What Is A Marriage Contract In Ontario?
A marriage contract is a legal agreement between two people who are married or about to get married. It’s also sometimes called a prenup or postnup, depending on when it’s signed — before or after the wedding. In Ontario, these contracts are governed by the Family Law Act.
So, what is a marriage contract, in practical terms?
It’s a written agreement that can cover things like:
- Who owns what property (now and in the future)
- How property will be divided if the marriage ends
- Whether spousal support will be paid
- How debts will be handled
- What happens to the family home in case of separation
Marriage contracts can’t include decisions about child custody or child support, since those must be determined based on the child’s best interests at the time of separation.
Are Marriage Contracts Legally Binding In Ontario?
Yes – but only if they meet certain legal requirements.
For a marriage contract to be considered valid and enforceable under Ontario law, it must:
- Be in writing
- Be signed by both parties
- Be witnessed
- Be made voluntarily, without pressure or coercion
- Include full and honest financial disclosure by both parties
While these contracts are legally recognized in Ontario, courts can set aside a marriage contract if it doesn’t meet legal standards or seems fundamentally unfair.
In other words, marriage contracts are legally binding — but not unbreakable.
Grounds to Challenge a Marriage Contract in Ontario
So, what makes a marriage contract invalid?
Ontario courts may overturn or “set aside” a marriage contract for several legal reasons. These challenges usually fall into two categories: how the contract was created (process) and what’s actually in it (content).
Let’s look at the most common grounds for challenging a marriage contract in Ontario:
Lack of Full Financial Disclosure
When signing a marriage contract, both people are expected to fully disclose their finances — that means assets, debts, income, and liabilities.
If one partner hid information — like owning a business, having large debts, or holding property — the agreement may be set aside.
Why it matters: You can’t make an informed decision without a clear picture of your partner’s financial situation. Courts take this very seriously.
No Independent Legal Advice
Although not legally required in most provinces, independent legal advice (ILA) is one of the best ways to protect the integrity of a marriage contract.
If only one person got legal advice, or if the other person didn’t fully understand the contract before signing, the court may decide it’s unenforceable.
At Jointly, we provide a certificate of independent legal advice with every agreement so that you can bring it to a lawyer in your area if you choose to. We believe in accessible, transparent legal education — but also know that having a lawyer’s input can make your agreement stronger. It is an added expense, but a good idea if you can afford it.
Duress or Pressure to Sign
A contract must be signed voluntarily. If one person felt pressured, coerced, or rushed into signing, the court may find that the agreement isn’t valid.
Examples of duress include:
- Signing just days before the wedding
- Threats to cancel the wedding unless the contract is signed
- Emotional or financial pressure
- A power imbalance (emotional, financial, or otherwise)
This is why it’s important to start early and allow time for both partners to reflect, ask questions, and get legal advice if needed. Starting the process of making your prenup a few months before the wedding at the latest is best practice.
Unfair or Unconscionable Terms
Even if a marriage contract meets all the legal requirements, it can still be set aside if the terms are grossly unfair or one-sided.
A court may ask:
- Does the agreement disproportionately benefit one person?
- Was the other person left without reasonable support or property?
- Were contributions to the relationship (like caregiving or career sacrifices) overlooked?
For example, if one spouse stayed home to care for children while the other built a successful business — and the contract gives the stay-at-home spouse nothing — a court may see that as unconscionable.
Fairness matters. Fairness doesn’t mean everything has to be perfectly equal but it does mean that both parties are treated with respect and dignity and have their contributions valued.
Significant Change in Circumstances
While courts don’t overturn marriage contracts lightly, they may do so if circumstances have changed so drastically that the agreement no longer makes sense.
Examples include:
- One partner becomes disabled or ill and can no longer work
- A major financial event occurs (e.g., inheritance, job loss, bankruptcy)
- Caregiving responsibilities evolve significantly
- One person made life-altering decisions based on the agreement that no longer hold
This is why it’s important to review and update your marriage contract after major life changes. We’ve included a review form with every Jointly agreement that you can sign with your partner every few years if your agreement still fits. If it doesn’t, you can change your prenup or make a new agreement any time if you both agree.
How Do Ontario Courts Decide if a Marriage Contract Is Enforceable?
Courts look at two main things when deciding whether to uphold or overturn a marriage contract:
1. Form
- Was the contract in writing, signed, and witnessed properly?
- Was it made voluntarily, without pressure?
- Was there full and honest financial disclosure?
- Was the language clear and understandable?
2. Substance
- Are the terms fair and reasonable, considering the couple’s unique situation?
- Did each party understand what they were agreeing to?
- Were both people treated with dignity and respect in the agreement?
The burden of proof is on the person challenging the marriage contract. That means they need to show that something about the agreement — or how it was created — was legally flawed or deeply unfair.
What Happens if a Marriage Contract Is Invalid?
If a court finds that a marriage contract is invalid or unenforceable, it won’t be used to settle financial issues. Instead, Ontario’s default family law rules will apply.
That typically means:
- Equal division of property acquired during the marriage
- Spousal support based on financial need and contribution
- Equal right to possession of the family home (even if only one person owns it)
These default rules are designed to be fair — but they may not reflect what you and your partner would have chosen.
This is why having a valid and thoughtful marriage contract matters. It gives you both more control over your financial future.
How to Protect a Marriage Contract from Being Challenged
If you’re thinking about creating a marriage contract — or reviewing one you already have — here are some steps you can take to reduce the risk of it being challenged in court:
- Disclose Everything: Be honest and thorough with your financial information.
- Avoid Rushed Signing: Don’t leave it until the last minute — start the conversation early.
- Use Clear Language: Make sure the agreement is written in plain, understandable terms.
- Aim for Fairness: The contract doesn’t need to be perfectly equal, but it should be reasonable and reflect the realities of your relationship.
- Get Independent Legal Advice: If you can afford it, each person should talk to their own lawyer before signing.
- Update When Needed: If your circumstances change significantly, revisit and revise the agreement.
At Jointly, we make it easy to build a clear, balanced, and legally-informed marriage contract that you can trust. Our platform walks you through the process step by step, and includes a certificate of legal advice that you can take to a lawyer in your area if you’d like.
Final Thoughts
A marriage contract in Ontario can be a powerful tool for protecting your future — but only if it’s done properly. If you’re wondering about challenging a marriage contract in Ontario, or want to make sure yours is solid, the key is transparency, fairness, and legal integrity.
Whether you’re starting from scratch or updating an existing agreement, Jointly can help. We offer an affordable and guided way to build a contract that reflects your values — and holds up in court.
Take control of your relationship’s future — together.
Start your marriage contract now at getjointly.ca.
I founded Jointly because I want to empower more Canadians with the knowledge and tools to create relationship agreements that work for them, at a price they can afford. My big dream? That reaching more Canadians with Jointly ultimately keeps more families out of the court system when relationships breakdown, which can be slow, expensive and traumatic. (I may or may not have personal experience with this 😅)
When I'm not lawyering, I'm most likely hiking with my dogs, kayaking the coastal waters around North Vancouver, or hitting the sauna and cold plunge.
- Challenging A Marriage Contract In Ontario - June 2, 2025
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