Shared blame and divided damages: what’s with Ontario’s Negligence Act?

When more than one person is at fault for an injury, things get complicated fast. In Ontario, its Negligence Act sorts out who owes what and to whom when fault is shared. For personal injury lawyers and litigants in Ontario, understanding how this short law operates in multi-party proceedings can help in building one’s case, protecting each’s rights, and in pursuing the right parties.

What does the Negligence Act say about fault in personal injury claims?

The Negligence Act (the Act) does two things at once: first, it protects plaintiffs, and second, it creates a framework through which defendants can sort out their respective liabilities among themselves.

Joint and several liability under the Negligence Act

Section 1 of the Negligence Act is where most of the action is. It says that where two or more people cause or contribute to damages, the court determines how much each is at fault.

As such, all defendants found at fault are jointly and severally liable to the plaintiff. In practice, it means that the plaintiff can collect the full judgment from any one defendant, regardless of how the fault percentages fall.

Example of applying joint and several liability

That matters enormously when one defendant is solvent and another is not. For instance, if Defendant A is 25 percent at fault and Defendant B is 75 percent at fault but has no assets, the plaintiff may still collect 100 percent of the judgment from Defendant A. Defendant A then pursues Defendant B separately for contribution.

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Contributory negligence under the Negligence Act

On the other hand, section 3 of the Negligence Act addresses what happens when the plaintiff shares some of the blame, commonly called contributory negligence.

The Act has eliminated the old common law rule that any fault on the plaintiff’s part would bar the entire claim. Now, fault is apportioned proportionally.

Examples of contributory negligence

The examples for applying contributory negligence are straightforward:

• damages assessed at $100,000; plaintiff found 25 percent at fault: award reduced to $75,000
• damages assessed at $200,000; plaintiff found 20 percent at fault: award reduced to $160,000
• damages assessed at $500,000; plaintiff found 10 percent at fault: award reduced by $50,000

When both parties are equally at fault

Section 4 of the Act handles situations where the court cannot assign specific percentages. In such a case, i.e., where it is not practicable to determine the respective degrees of fault, all parties are deemed equally at fault.

This default rule is a practical backstop and not just a presumption. It means that it only applies where the evidence truly does not support a more precise split.

In actions tried by a jury

In jury trials, section 6 of the Act gives the fault-finding role to the jury rather than the judge. While the judge instructs on the law, it is the jury that assigns the numbers.

As confirmed in Patterson v. Peladeau, 2018 ONSC 2625, those numbers are inherently judgment calls. In this case, the Ontario Superior Court dismissed the mistrial motion and found, among others, that the jury’s 73 percent–27 percent apportionment between the plaintiff and the defendant was well supported by evidence.

How can contribution claims be pursued under the Negligence Act?

While section 1 of the Negligence Act creates the entitlement to contribution and indemnity between tortfeasors, section 2 governs how that right is exercised after a settlement.

Under the law, a defendant who settles with the plaintiff can still pursue contribution or indemnity from another tortfeasor who would have been liable had they been sued. However, there’s a catch to this:

• the settling defendant must satisfy the court that the settlement amount was reasonable, and
• if the court finds that the amount was excessive, it has authority to fix the amount at which the claim should have been settled

In litigation, this becomes a real risk, since a defendant who overpays on a settlement to close the file quickly may find their contribution claim reduced accordingly.

What the contribution mechanism means strategically

The contribution mechanism means that even a settling defendant is not necessarily done. The interplay between sections 1 and 2 creates several strategic pressure points:

• a defendant who settles early should document the reasonableness of the settlement amount carefully, with reference to liability exposure and damages evidence at the time of settlement
• a defendant who refuses to settle may face the risk that a co-defendant settles and then pursues them for contribution
• the threat of a contribution claim can itself influence whether parties resolve the original action, and on what terms

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What are the steps to add third-party defendants in a personal injury claim?

Section 5 of the Negligence Act creates the substantive right to bring new parties into proceedings. It says that wherever a person not already part of the action appears to be wholly or partly responsible for the damages claimed, that person may be added as a party defendant or made a third party to the action under the rules of court.

Two options in adding third-party defendants

There are two procedural routes that are available under section 5:

• adding as a party defendant: the new party is joined directly to the main action, with full exposure to the plaintiff’s claim
• third-party procedure: the existing defendant brings a separate claim against the new party, which runs alongside the main action under the Rules of Civil Procedure

The threshold for invoking section 5 is deliberately low. The person need only to “appear” to be “wholly or partly responsible.” This means that a defendant does not need to prove the third party’s liability before bringing them in.

A web of pleadings when adding third-party defendants

In complex personal injury matters, this mechanism can generate a chain of claims. The plaintiff sues the defendant; the defendant brings a third-party claim; the third party brings a fourth-party claim; and so on. Those that are particularly prone to this kind of litigation structure are:

• collisions involving several vehicles
• construction site injuries
• medical negligence against multiple care providers

Personal injury lawyers on either side of these cases should move early on third-party claims. If a co-defendant settles before the third party’s role is assessed, the section 2 contribution mechanism may still be available, but the evidentiary foundation becomes harder to build after the fact.

Costs are also relevant. Section 7 of the Act gives courts discretion to direct that a contributorily negligent plaintiff bears some portion of the costs where the circumstances make this just. In multi-party cases where the plaintiff’s own conduct is a significant factor, defendants should keep this provision in mind when assessing overall exposure.

How do courts decide on apportionment in successive personal injury cases?

Fault apportionment becomes most complex in cases involving successive tortfeasors. These are situations where the plaintiff is injured by one defendant, and then injured again (or has their first injury worsened) by a second, separate act of negligence.

Is the injury divisible or indivisible?

The core question in this case is whether the injury is divisible or indivisible. If it is indivisible, i.e., the harm cannot be cleanly attributed to one tortfeasor over another, the courts apply principles drawn from the Supreme Court decision in Athey v. Leonati, [1996] 3 SCR 458.

Athey established that a defendant’s negligence does not need to be the only cause of an injury to attract full liability. Where negligence caused or contributed to an indivisible injury, the defendant can be responsible even if other contributing factors were also present.

How Athey applies in personal injury case

The case of Lyng v. Ontario Place Corporation, 2024 ONCA 23, illustrates how this plays out at the trial and appellate levels.

In Lyng, the plaintiff was found 25 percent contributorily negligent, yet still succeeded because the defendant was found primarily responsible. The apportionment survived appellate review, reinforcing that a finding of contributory negligence does not defeat the claim; rather, it just reduces the award.

Successive harm and the defendant’s contribution

In multi-defendant cases involving successive harm, courts conducting apportionment under section 1 of the Negligence Act must assess each defendant’s contribution to the overall injury.

The Ontario Court of Appeal confirmed the four required elements of a negligence claim in Case v. Pattison, 2023 ONCA 529:

• duty of care
• breach of the standard of care
• compensable damage
• causation

Where causation is contested across multiple defendants, the apportionment exercise becomes the central battleground at trial.

Negligence Act: what happens when fault is shared

Ontario’s Negligence Act may be short, but it carries a long reach. Like the claims it governs, the consequences of getting it wrong tend to spread in multiple directions. Whether it is for building a multi-party case for a plaintiff, protecting a solvent defendant against a contribution shortfall, or deciding when to move on a third-party claim, the Act’s provisions set the terms. Knowing those terms, and acting on them early, is what separates a well-constructed personal injury file from one that catches counsel off guard at trial.

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