Mistake of Law
Mistake of law is, as a general rule, not a defence to a criminal charge in Canada. Section 19 of the Criminal Code codifies the maxim ignorantia juris non excusat — ignorance of the law is no excuse. A person who acts in good faith on a mistaken understanding of what the law requires or permits is still criminally responsible for conduct that breaches the law. The principle reflects the practical impossibility of administering criminal law if every accused could plead ignorance.
Mass Tsang's criminal lawyers handle mistake-of-law issues in regulatory, tax, and certain professional-conduct contexts. For more, see our blog post on mistake of fact and mistake of law.
Narrow exceptions
Although the general rule is strict, the Supreme Court has recognized narrow exceptions. The doctrine of "officially induced error" provides a defence where: (1) the accused considered the legal consequences of their actions; (2) the accused sought legal advice from an official responsible for administering the relevant law; (3) the official provided erroneous advice; (4) the accused relied on the advice; (5) the reliance was reasonable; and (6) the accused acted accordingly. The defence is rarely successful but is available in principle. The leading case is R v Jorgensen, 1995.
Colour of right
In property offences, "colour of right" — a genuine belief in a legal right to the property — operates as a defence. The belief can be based on mistaken understanding of either fact or law. In a theft case, for example, an accused who honestly believes they are entitled to take the property (because they think it is their own, or because they think they have a legal claim against the owner) is not guilty of theft. The defence is distinct from the strict bar on mistake of law and is firmly established.
Mistake of fact vs. mistake of law
The line between mistake of fact and mistake of law can be subtle and is often determinative. A belief about what conduct the law prohibits is mistake of law (no defence). A belief about the facts that determine whether the law applies is mistake of fact (potential defence). For example: a belief that a substance is not a drug — mistake of fact. A belief that selling that drug is legal — mistake of law.
Charter and remedial possibilities
While mistake of law is not a substantive defence, abuse of process arising from misleading state conduct can support a Charter remedy under section 7. Where state actors (including police, prosecutors, or regulators) actively misled an accused about the legality of conduct, a stay of proceedings is sometimes available. The remedy is exceptional and reserved for the most extreme cases.
Strategic implications
Mistake-of-law arguments rarely succeed as defences but can be relevant to sentencing as mitigating context — an accused who acted in good faith on a misunderstood legal framework is morally less blameworthy than one who acted with full knowledge of illegality. Counsel should not confuse the substantive bar with the relevance of context to mitigation.
Related glossary terms
