The Implied Undertaking Rule in Ontario: Why You Can't Use Discovery Evidence Outside the Lawsuit

You just spent months exchanging documents and sitting through examinations for discovery in a lawsuit. Somewhere in that pile is a document that would be very useful in an entirely different dispute — maybe against the same person, maybe against someone else. Can you use it? In Ontario, the answer is usually no, and the reason has a name: the implied undertaking rule.

This rule surprises a lot of litigants because nothing about it is written into the documents they signed. It exists automatically, by operation of law, the moment discovery happens in a civil case.

What the Implied Undertaking Rule Says

When parties to an Ontario lawsuit exchange documents and give evidence at examinations for discovery, they are required to do so — the process isn't voluntary. In exchange for that compelled disclosure, the law treats every party as having made an implicit promise: material obtained through discovery will only be used for the purposes of that specific lawsuit, and not for anything else.

In practice, this means a document, an admission, or testimony given at discovery in Case A generally cannot be used:

• In a different lawsuit against the same party
• In a lawsuit against a completely different party
• For business, media, or personal purposes unrelated to the litigation
• To pressure or embarrass the other side outside the courtroom

The rule applies whether or not anyone actually labelled the material "confidential." It attaches automatically because of how the material was obtained.

Why the Rule Exists

Discovery in Ontario is unusually broad — parties are generally required to produce documents and answer questions about matters relevant to the case, even material they would rather keep private. That level of disclosure only works if people can trust it won't be turned against them in unrelated contexts.

The implied undertaking rule is the trade-off that makes broad discovery possible: you have to disclose relevant material to the other side, but they can't then take that material and use it as a weapon somewhere else. Without this protection, litigants would have a strong incentive to resist producing documents and to answer discovery questions as evasively as possible.

What Counts as "Outside the Lawsuit"

The rule isn't limited to obviously improper uses. Examples of what typically falls outside the permitted purpose include:

• Filing discovery material in a different court proceeding, even one that seems related
• Sharing discovery documents with a journalist, competitor, or regulator
• Posting discovery evidence publicly or using it in a public dispute
• Providing discovery material to a person who is not a party to the original action, without permission

The key question is always whether the use relates to the specific lawsuit in which the material was obtained. If it doesn't, the rule generally still applies even after that lawsuit has ended.

Exceptions: When You Can Use Discovery Material Elsewhere

The implied undertaking rule is not absolute. Material used or referred to during an open court proceeding — for example, read into evidence at trial, or filed as part of a motion argued in open court — generally loses its protected status, since court proceedings and their records are generally open to the public.

A party can also apply to the court for permission to use discovery material for another purpose. Courts weigh the reason for wanting to use the material against the interests the rule protects, and outcomes depend heavily on the specific facts, so this isn't something to assume will be granted.

What Happens If You Break the Rule

Because the implied undertaking rule exists automatically, breaching it is treated seriously even if no one signed an explicit confidentiality agreement. A party who misuses discovery material can face:

• A contempt of court finding
• Cost consequences in the original or related proceeding
• An order restricting further use of the material
• Damage to their credibility in the eyes of the court on other issues in the case

Given how easy it can be to breach the rule without realizing it — forwarding a document, mentioning testimony in an unrelated conversation, referencing it in another proceeding's pleadings — anyone handling discovery material from an Ontario lawsuit should treat it as confidential by default.

Frequently asked questions