Can I bring a third party into an existing Ontario lawsuit?

Yes, in Ontario a defendant in a lawsuit can bring in a third party — someone not already a party to the action — by issuing a Third Party Claim under Rule 29 of the Rules of Civil Procedure. This is done when the defendant believes that if they are found liable to the plaintiff, the third party should be required to indemnify or contribute to that liability.

Common examples include: a contractor sued by a homeowner who then issues a third party claim against a subcontractor whose deficient work caused the problem; or a corporate defendant claiming indemnity from an officer or director responsible for the alleged wrongdoing.

The third party claim functions like a mini-lawsuit within the main action. The third party is served and has the right to defend both against the defendant's claim and, in some cases, against the plaintiff's original claim. Third party proceedings can add complexity and cost to a lawsuit, but they allow all related claims to be resolved in a single proceeding, avoiding inconsistent judgments and duplicated litigation. Third party claims must be issued within specific time limits set out in the rules, and any limitation period arguments by the proposed third party must be considered before the claim is issued. Speak with a lawyer about whether a third party claim is appropriate and timely in your situation.