Can I change or add to my statement of claim after it has been filed in Ontario?

Yes, parties in Ontario can amend their pleadings, but the rules become stricter the further along the litigation has progressed. Early in the proceeding, a party can amend a pleading once without leave (permission) of the court, as long as no discovery has taken place and the amendment does not require an extension of time.

Once discovery has started or the amendment would prejudice the other side, you generally need to bring a motion to amend and obtain the court's permission. Courts will consider whether the amendment is genuinely necessary, whether it would cause unfair delay or prejudice, and whether it raises a new claim that might be statute-barred.

Adding entirely new parties or new causes of action after the limitation period has expired is difficult and sometimes impossible. The court balances the importance of allowing parties to present their full case against the opposing party's right not to be ambushed by new issues late in the litigation. If you realize your pleadings need to be updated, act as early as possible and get your lawyer involved promptly.