Crossclaims Between Co-Defendants in Ontario: How They Work

You have been named as one of several defendants in an Ontario lawsuit, and privately you are convinced the person sitting next to you at the defence table is really the one at fault. Ontario's civil process lets you say so formally, without waiting for the main case to finish first. A crossclaim ontario co-defendants file lets one defendant make a claim directly against another defendant in the same lawsuit — for indemnity, contribution, or a separate but related claim.

A crossclaim only runs between parties already on the same side of the existing action (typically co-defendants, though the same idea can apply between co-plaintiffs in limited situations). It is distinct from suing an outsider who was never part of the case, and distinct from a defendant's claim back against the plaintiff.

Crossclaim, Counterclaim, and Third Party Claim — How They Differ

When a Crossclaim Makes Sense

• Multiple defendants, disputed fault between them. A common scenario is a multi-vehicle accident, or a construction project with several contractors, where the plaintiff has sued everyone potentially involved, and the defendants privately disagree about who actually caused the loss.
• One defendant has an indemnity right against another. A contract, insurance arrangement, or other legal basis may mean one co-defendant is entitled to be repaid by another if held liable.
• Avoiding a second lawsuit after the first one finishes. Without a crossclaim, a defendant who ends up paying the plaintiff might otherwise have to start an entirely new action against the co-defendant afterward to recover a contribution — a crossclaim resolves that within the same case.

How the Process Generally Works

1. A defendant who wants to crossclaim against a co-defendant files the crossclaim, typically alongside their statement of defence, setting out the basis for the claim against the co-defendant.
2. The co-defendant being crossclaimed against is served and gets to file a defence to the crossclaim, just as with any other claim.
3. The crossclaim proceeds alongside the main action — generally with the same trial, the same evidence, and the same overall timetable, though the court retains case-management discretion.
4. At the end of the case, if the plaintiff succeeds against multiple defendants, the crossclaims determine how responsibility (and any payment) is allocated among those defendants themselves.

Why Resolving This in One Proceeding Matters

Litigating shared fault in a single action, rather than through follow-up lawsuits after the main case ends, has real practical advantages:

• One trial, one set of findings. A judge or jury who hears the whole story at once is far less likely to reach inconsistent conclusions about what caused the loss than separate proceedings might produce years apart.
• Costs efficiency. Evidence, examinations, and expert reports are frequently shared across the crossclaim and the main action rather than duplicated.
• Finality. Once the case concludes, the allocation of responsibility between co-defendants is generally settled at the same time as the plaintiff's claim, rather than remaining an open question.

A Few Practical Limits

• A crossclaim, like any pleading, must actually disclose a legally recognized basis for the claim — a co-defendant cannot simply be named out of frustration with no underlying legal theory.
• The crossclaiming defendant still has to prove its case against the co-defendant on the evidence; the plaintiff's success against both defendants does not automatically resolve how they should split responsibility between themselves.
• If a co-defendant crossclaimed against is dismissed from the plaintiff's main claim entirely, the crossclaim may still continue independently if it raises its own distinct basis for relief.

Frequently asked questions