Ex Post Facto Definition and Legal Meaning

On this page, you'll find the legal definition and meaning of Ex Post Facto, written in plain English, along with examples of how it is used.

What is Ex Post Facto?

adj. Latin for “after the fact,” which refers to laws adopted after an act is committed making it illegal although it was legal when done, or increasing the penalty for a crime after it is committed. Such laws are specifically prohibited by the U.S. Constitution, Article I, Section 9. Therefore, if a state legislature or Congress enacts new rules of proof or longer sentences, those new rules or sentences do not apply to crimes committed before the new law was adopted.