What Mistake of Law Means in a Criminal Case

The common saying that “ignorance is bliss,” does not apply when talking about ignorance of the law in a criminal case. The difference between “mistake of law” and “mistake of fact” is an important concept for understanding the mechanics of a criminal defense. Although mistake of fact can be a valid defense to a criminal charge, a mistake of law is typically not.

What is a Mistake of Law

A mistake of law is when a person does something that is illegal but states that he did not know the act was illegal at the time. The law does not allow this person to escape criminal liability with this excuse, except for very rare exceptions. The underlying expectation is that everyone is aware of the law of the land and cannot plead ignorance of the law as an excuse for criminal activity. These are some of the rare exceptions where a mistake of law defense may apply. It is important to note that these exceptions may not apply in all jurisdictions, which is why it is recommended to consult with an attorney if you have been charged with a crime.

Reversed Court Decisions

If the defendant can prove that he relied on information from the government, and in particular a court decision that was overturned before the defendant committed the illegal act, then a mistake of law defense may apply.

Specific Intent Requirements

This situation typically involves violations of the tax code, such as willfully filing a false income tax return. Because of the complex nature of the tax code and the requirement that the defendant understand that he was violating the code at the time of the filing, proving that you had no knowledge of the requirement or misunderstood its application, can be a valid defense for a tax code violation.


Conspiracy means that the defendant was involved with a group of people that intended to work together to commit and illegal act. The crime of conspiracy requires that the defendant understand that the ultimately activity was illegal, so if the defendant can prove he had no knowledge of that, then he may have a valid defense.

While there are other scenarios where a mistake of law defense may apply, this is an extremely limited defense, which must be proven by the defendant in order to excuse him from liability of a crime. It is important to consult with an attorney if you think any of these situations may apply to you.