Also known as: postfacto · ex post facto
Written by attorneys · grounded in primary & secondary sources — see below
Legislation that retroactively alters the legal consequences of past conduct by criminalizing acts that were lawful when performed or by increasing the punishment attached to completed offenses.
Peter Park completed a series of sales last year that were lawful under then-existing state law. After a new administration took office, the legislature passed a statute making those exact sales criminal and directing that the new penalties apply to all prior transactions. Peter faces prosecution under the new statute for conduct that carried no criminal liability when he acted.
Priya Prasad was investigated for an alleged offense five years ago, but the statute of limitations expired without charges. The legislature then enacted a new law extending the limitations period and expressly reviving all previously time-barred prosecutions. Prosecutors now seek to charge Priya under the revived limitations period for the same past conduct.
Select any source to read its text and confirm it supports the definition.
Pierce Patterson engaged in conduct that federal law treated as a misdemeanor at the time. Congress later passed a statute reclassifying the same conduct as a felony with substantially higher maximum and mandatory minimum sentences and directed that the new penalties apply to all prior violations. Pierce is now sentenced under the harsher scheme.
Pamela Phillips was tried and convicted under state procedures that allowed certain defenses. After her conviction became final, the state supreme court adopted a new interpretation that eliminated one of those defenses and applied the change retroactively to cases already decided. Pamela seeks to challenge the retroactive application of the new rule to her completed trial.
Perry Pratt committed a capital offense under a statute later invalidated by the Supreme Court. The legislature enacted a new capital sentencing statute that applies to offenses committed before its passage. Perry argues that the new statute cannot govern his case because it was adopted after the crime occurred.
Priscilla Parks held a position with a regulated entity before a new federal statute took effect. The statute bars anyone who previously held such a position from future employment in the same field and applies the bar to conduct that occurred before the statute was enacted. Priscilla is denied a license renewal solely on the basis of her pre-statute employment history.
The clause bars Congress and the states from enacting laws that retroactively make conduct criminal, increase the punishment for completed offenses, or alter rules of evidence to make conviction easier after the fact.
Yes. The clause targets penal legislation. Civil regulatory measures are generally outside its scope unless they are so punitive in purpose or effect that they function as criminal punishment.
No. Extending a limitations period after it has already expired and applying the extension to previously time-barred offenses violates the Ex Post Facto Clause because it reopens the possibility of punishment for past conduct.
No. Only those changes that increase the quantum of evidence needed for conviction or otherwise disadvantage the defendant in a manner that alters the legal consequences of past conduct are prohibited. Purely procedural changes that do not increase punishment are generally permissible.
…a measure was "necessary and proper" to the discharge of its substantive legislative authority, pass a bill of attainder or ex post facto law contrary to the prohibitions contained in § 9 of Art. I. No more may it vest in itself, or in its officers, the authority to appoint officers of the United States when the Appointments…