Challenging a Will for Lack of Testamentary Capacity in Ontario: What You Need to Know

You've just learned that a parent, spouse, or close relative left a will that seems completely out of character — or that cuts out family members in a way that makes no sense given everything you knew about them. Maybe they were diagnosed with dementia in the months before signing. Maybe a new caregiver appeared and the estate plan changed overnight. Whatever the circumstances, one question keeps surfacing: did they actually have the mental capacity to make this will?

Challenging a will for lack of testamentary capacity in Ontario is one of the most common — and most difficult — grounds for a will contest. The courts take a high bar before setting aside a will, and the legal process can be long. But when the evidence is there, a successful challenge can restore what the law — and the person you knew — would have intended.

This article explains how the capacity test works, who can bring a challenge, what evidence matters, and what happens if a court agrees the will is invalid.

What Is Testamentary Capacity?

Testamentary capacity is the legal standard a person must meet at the moment they sign their will. It is not the same as being diagnosed with a medical condition — a person can have dementia and still have capacity on a good day. Equally, someone who appears sharp can lack capacity in legally meaningful ways.

Ontario courts follow the common law test that has been applied across Canadian provinces for well over a century. To have testamentary capacity, the person making the will (called the testator) must, at the time of signing:

1. Understand the nature of a will and its effects — they must know they are signing a document that gives away their property after death.
2. Know the extent of their property — they do not need a precise accounting, but they must have a general grasp of what they own.
3. Recognize the people who have a natural claim on their estate — typically a spouse, children, or other close dependants. The testator does not have to leave anything to them, but must know who they are and have consciously decided what to do.
4. Not be suffering from a "disorder of the mind" that poisons their affections, perverts their sense of right, or prevents the exercise of their natural faculties — in plain language, a mental illness or condition must not have distorted the will itself.

All four elements must be present together. A gap in any one of them can render the will invalid.

Signs That Capacity May Have Been Absent

No single symptom proves incapacity, but certain patterns regularly appear in successful challenges:

• A diagnosis of Alzheimer's disease, vascular dementia, or another cognitive condition around the time the will was signed
• Hospital or care home records documenting confusion, disorientation, or an inability to recognize family members
• A dramatic and unexplained change in the will — particularly one that benefits a new person who entered the testator's life shortly before signing
• Accounts from family, friends, or health workers describing the person as confused, easily led, or unable to hold a coherent conversation
• A will signed without a lawyer, or where the lawyer had no meaningful conversation with the testator before execution

These are starting points for investigation, not proof. Courts look at the totality of the evidence.

Who Can Challenge a Will in Ontario?

Ontario's Succession Law Reform Act governs who has standing to challenge an estate. Generally, a challenge can be brought by:

• A beneficiary named in the challenged will
• A beneficiary under a prior will that would take effect if the new one is set aside
• A person who would inherit under the intestacy rules (the rules that apply when someone dies without a valid will) if no will stands
• A dependant of the deceased who has a claim for support

If you are unsure whether you have standing, that is the first question to put to a lawyer.

How to Start a Challenge in Ontario

Will challenges are heard in the Ontario Superior Court of Justice — Estates List (in Toronto and certain other regions) or in the local Superior Court. The process generally unfolds in several steps:

1. Obtain a copy of the will. Once a will is probated — granted a Certificate of Appointment of Estate Trustee — it becomes a public court document. If probate has not yet been granted, you can file a caveat (also called a Notice of Objection) with the court to stop the estate trustee from obtaining the certificate while you investigate.
2. Gather evidence. This phase is time-intensive. You will need medical records, pharmacy records, and clinical notes from around the time the will was signed. Sworn statements (affidavits) from family members, caregivers, and anyone who witnessed the testator's condition are crucial. The lawyer or notary who drafted and witnessed the will may be compelled to disclose their file, including any notes of their capacity assessment.
3. Serve and file a notice of application. Once you have enough evidence to support the claim, your lawyer will commence the formal court proceeding.
4. Discovery and cross-examination. Both sides exchange documents and may cross-examine witnesses. Expert evidence from a geriatric psychiatrist or neurologist — interpreting the medical records against the legal capacity test — is often decisive.
5. Hearing or trial. A judge reviews all the evidence and decides whether the will stands.

As of writing, Ontario has a general two-year limitation period for civil claims, but will challenges have their own procedural timelines and the timing of filing a caveat matters. Verify current rules with a lawyer before any deadline passes.

Who Bears the Burden of Proof?

Ontario courts start with a presumption that a will is valid. The person challenging the will therefore carries the initial burden of showing there is a genuine issue about capacity — enough to require the proponent of the will (usually the estate trustee) to prove that capacity existed.

Once that threshold is crossed, the burden shifts. The estate trustee must satisfy the court, on a balance of probabilities, that the testator had capacity at the moment of signing. Expert medical evidence, the drafting lawyer's notes, and contemporaneous accounts of the testator's condition all become central to this analysis.

What Happens if the Challenge Succeeds?

If a court finds the will invalid for lack of testamentary capacity, it is treated as though the will never existed. The estate is then distributed according to:

• A prior valid will, if one exists and is admitted to probate; or
• The intestacy provisions of the Succession Law Reform Act, which set out a fixed order of inheritance for spouses, children, and other relatives.

The court may also make orders about costs. Will challenges are expensive for everyone involved, and judges have broad discretion about how legal fees are allocated across the estate.

Frequently asked questions