Is a will valid in Ontario if it was only signed by one witness?

Generally, no. A formal will in Ontario must be signed by the testator (the person making the will) in the presence of two witnesses, who must also sign the will in the testator's presence. A will witnessed by only one person does not meet the formal requirements under the Succession Law Reform Act and is typically invalid.

There is one important exception: a holograph will, which is entirely handwritten and signed by the testator in their own handwriting, does not require any witnesses at all. But a typed or partially printed will almost never qualifies as a holograph will and must have two witnesses.

If a court finds that a will is invalid — whether because of a missing witness, improper signing, or another deficiency — the estate is treated as if the person died without any will at all, and the intestacy rules apply. Some jurisdictions allow courts to cure minor defects, but Ontario's current rules on curing defects are limited. A properly drafted and executed will, prepared with legal guidance, avoids these risks.