How long do I have to sue someone in Ontario before losing the right to claim?

In Ontario, the basic limitation period for most civil claims is two years from the date you discovered (or reasonably should have discovered) that you had a claim. This is established by the Limitations Act, 2002. If you do not start your lawsuit within that two-year window, the defendant can raise the expired limitation period as a complete defence, and your claim will generally be dismissed regardless of its merits.

The two-year clock typically begins not on the date the wrong occurred, but on the date you knew or ought to have known: that the harm happened, that it was caused by an act or omission, that the defendant was responsible, and that a lawsuit would be an appropriate way to address it. This is called the "discoverability" principle.

There is also an ultimate limitation period of 15 years from the date the act or omission occurred, regardless of when you discovered the claim. This means that even if you did not discover your claim until year 14, you have at most one year left to sue. Certain claims have their own special limitation periods — for example, claims involving government defendants, sexual assault survivors, and others — so it is important to confirm which rule applies to your specific situation with a lawyer.