On what grounds can a will be contested in Ontario?

In Ontario, a will can be challenged in court on several established legal grounds. The most common are: lack of testamentary capacity, undue influence, fraud, and improper execution.

Lack of testamentary capacity means the person who made the will did not have the mental ability required at the time of signing. In Ontario, a testator must understand the nature of a will, know the general extent of their property, recognize who their natural heirs are, and appreciate that these elements all come together in the document being signed. A diagnosis of dementia or cognitive impairment does not automatically mean there was no capacity — courts look at the person's condition at the specific time the will was signed.

Undue influence means someone pressured or manipulated the testator into making the will they wanted rather than one the testator freely chose. This is harder to prove than capacity issues and requires showing that the influence amounted to coercion — something beyond ordinary persuasion or suggestion.

Fraud occurs when the testator was deceived about the nature of the document they were signing, or about material facts affecting their decisions. Improper execution means the formal requirements of the Succession Law Reform Act — such as having two witnesses present who are not beneficiaries — were not met.