This article titled ‘Ex Post Facto: Meaning, Explanation and Case Laws .’ is written by Sahajpreet Bhusari and discusses the doctrine of ex post facto.
I. Meaning and Origin
Ex post facto is a legal term of Latin origin. It literally means ‘from a thing done afterwards’.
Ex post facto law refers to a law that has a retrospective effect on an act that was legal or not prohibited by law before the enactment of the law.
When any law is enacted it can have either prospective effect or retrospective effect. Prospective laws are laws effective in future which means they will only be applicable on cases that occur after the enactment of the law. Retrospective or ex post facto laws affect the legal position and consequences before the enactment of the law.
Article 20 (1) of the Indian Constitution prevents the legislature from framing ex post facto laws concerning criminal nature. It basically is protection from ex post facto laws. No person can be held guilty for an act that was not considered to be illegal at the time of commission and no person can be asked to pay a penalty more than what is prescribed by the law at that point in time.
However, it can work the other way. For that let us understand the rule of beneficial interpretation. It states that if the retrospective law is in benefit of the accused, then the accused will be made available all the remedies under the new law.
IV. Important Case Laws
It was in the case of West Ramnad Electronic Distribution Co. Ltd. v. State of Madras that the court held that the term “law in force” is not inclusive of retrospective laws.
In the case of Calder v. Bull the Supreme Court of United States explained that ex post facto laws are nay laws that criminalize actions that were not considered criminal actions when they actually took place or that provides a greater punishment as compared to the current law.
In the case of Kedar Nath v. State of West Bengal, the accused committed an offence which was then punishable by imprisonment or fine or both. However, two years later an amendment to the act enhanced the amount of fine and the Supreme Court, in this case, held that the enhanced punishment will not be applicable in this case.
 Rattan Lal v. State of Punjab, AIR 1965 SC 444.
 1952 AIR 75.
 1 L Ed 648.
 AIR 1953 SC 404.