By Z Legal Professional Corporation – Estate Litigation Lawyers in Toronto
Undue influence is frequently alleged in Ontario will challenges, particularly where a will benefits one family member disproportionately or is made late in life. However, the legal test for undue influence in the context of a will is significantly stricter than in lifetime (inter vivos) transactions.
Ontario courts have repeatedly emphasized that there is no presumption of undue influence in wills, and the burden of proof remains squarely on the party attacking the will.
This article explains how undue influence is proven in will challenges, how it differs from other estate disputes, and why these claims are among the most difficult to succeed on.
Who Bears the Burden of Proving Undue Influence in a Will Challenge?
In Ontario, the legal burden of proving undue influence in a will challenge rests entirely with the person attacking the will.
This principle has been consistently affirmed by the Supreme Court of Canada and Ontario courts, including:
- Vout v. Hay, [1995] 2 SCR 876
- Neuberger v. York, 2016 ONCA 191
- Seguin v. Pearson, 2018 ONCA 355
- Milner v. Milner, 2024 ONSC 4232
- Issa v. Aiello, 2025 ONSC 4055
The burden must be met on a balance of probabilities, meaning the court must be satisfied that undue influence is more likely than not to have occurred.
No Presumption of Undue Influence Applies to Wills
A critical distinction in Ontario estate law is that presumptions of undue influence do not apply to wills.
Unlike lifetime gifts or real estate transfers—where certain relationships can automatically shift the burden of proof—will challenges do not benefit from any rebuttable presumption of undue influence.
Ontario courts have been explicit on this point:
- A presumption of undue influence does not arise in wills
- The doctrine applicable to inter vivos transactions does not carry over into testamentary law
(Zerbinati v. The Children’s Lawyer; Seguin v. Pearson; Birtzu v. McCron)
This makes undue influence claims in will challenges far more difficult than many litigants expect.
The Role of Suspicious Circumstances
While suspicious circumstances are often present in contested estates, they do not shift the burden of proving undue influence.
Examples of suspicious circumstances may include:
- A dramatic change in testamentary intentions
- Isolation of the testator
- A beneficiary’s involvement in drafting the will
- Cognitive decline or dependency
However, even where suspicious circumstances exist, the legal burden of proving undue influence remains with the challenger (Vout v. Hay; Milner v. Milner).
What Suspicious Circumstances Can Do
Although suspicious circumstances do not assist with undue influence directly, they can shift the burden on other issues, including:
- Due execution of the will
- Knowledge and approval
- Testamentary capacity
In those circumstances, the propounder of the will may be required to prove that the will was properly executed and that the testator understood and approved its contents.
That said, even if suspicious circumstances raise concerns about fraud or influence, they do not relieve the challenger of the obligation to prove undue influence itself.
What Level of Influence Invalidates a Will?
The level of influence required to invalidate a will is exceptionally high.
Ontario courts have consistently held that:
- Persuasion is not enough
- Influence alone is insufficient
- The influence must rise to the level of coercion
To succeed, the evidence must establish that:
The influence was so overwhelming that the will reflects the intentions of the influencer, not the deceased.
(Poitras Estate v. Poitras)
This requires proof of actual coercion—meaning the effective domination of the testator’s free will (Milner v. Milner).
Evidentiary Challenges in Undue Influence Claims
Undue influence is rarely proven through direct evidence. However, Ontario courts have made clear that:
- Uncorroborated evidence is generally insufficient
- Independent evidence is usually required
- Speculation, suspicion, or opportunity alone will not meet the threshold
As confirmed in Milner v. Milner, courts require clear, convincing, and corroborated evidence before invalidating a will on the basis of undue influence.
Why Undue Influence Claims in Wills Are Difficult
From a litigation perspective, undue influence claims in wills are challenging because:
- There is no presumption to rely on
- The standard is coercion, not influence
- The testator is no longer available to testify
- The burden never shifts
As a result, these claims must be carefully assessed before being advanced.
Strategic Considerations in Will Challenges
Given the high threshold, experienced estate litigators often examine whether other grounds may be stronger, such as:
- Lack of testamentary capacity
- Failure of due execution
- Lack of knowledge and approval
- Fraud or forgery
Undue influence is often pleaded in conjunction with, rather than instead of, these claims.
Speak With an Ontario Estate Litigation Lawyer
If you are considering challenging a will—or defending one—on the basis of undue influence, early legal advice is essential. These cases turn on subtle factual and evidentiary issues, and missteps can be costly.
Z Legal Professional Corporation is a Toronto-based estate litigation firm with extensive experience in:
- Will challenges
- Undue influence claims
- Suspicious circumstances analysis
- Capacity disputes and estate trials
Contact Z Legal today to speak with an experienced Ontario estate litigation lawyer.