What was the first law struck down by a court?

As above, any jurisdiction.

Also, if a law holding someone has been found to be unconstitutional, are there any cases (aside from Ireland) where the people jailed under the law are still in jail?

In the US, it was Marberry vs. Madison in 1803, which struck down the Judiciary Act of 1789.

The Supreme Court in Marbury v. Madison didn’t strike down the entire Judiciary Act, 1789. It only addressed one part of s. 13 of the Act, which purported to give the Supreme Court the original jurisdiction to issue writs of mandamus. The Court held that Congress could not give original jurisdiction to the Supreme Court. The rest of the Act was left unaffected by the decision.

Getting back to the OP, two cases of the English Court of Common Pleas, both decided in 1610, are often cited as examples of a court striking down a law, although there are some ambiguities about characterising them in that way.

In Case of Proclamations, the Court held that a proclamation issued by King James I under the Royal Prerogative was not within the scope of the King’s authority. Since the Crown does have some legislative power under the prerogative, that may be interpreted as a case of striking down a law.

The other case is Dr. Bonham’s Case, in which the Court held that the English College of Physicians could not rely on a statute passed by Parliament as authority for it to imprison one of its members, Dr. Bonham. Based on the language Lord Coke used in his judgment, that case may be interpreted as saying that the courts could rely on the common law to strike down portions of an Act of Parliament that are contrary to reason and natural justice. However, other aspects of Lord Coke’s judgment could be interpreted as simply saying that he was strictly construing the statute in favour of the liberty of the individual, a standard principle of statutory interpretation.

Even if these two cases do not match modern conceptions of judicial review, they are usually cited as key cases in the development of the concept, which the American colonists later used in developing their political theories of limited government.

Judicial Review Before Marbury (Warning: PDF). At least 17 laws were invalidated by various courts as violative of a superior law, including but not limited to the Constitution. Marbury is seminal in being the first case in which (a portion of) an Act of Congress was declared to be null and void as against the Constitution.

When the Irish Supreme Court decided in A v Governor of Arbour Hill Prison* that a declaration of unconstitutionality didn’t automatically amount to a get-out-of-jail-free card, they did so in part by reference to case law in other jurisdictions. So the answer is most likely “yes”, though I don’t know the specifics of the cases they examined.

*For the Irish dopers, that was one that arose after the statutory rape law was struck down a few years ago.

Thanks very much for this link, Polycarp - very interesting indeed.

Just thought of another one: in Campbell v. Hall (1774), Lord Mansfield in the Court of King’s Bench held that a tax imposed by the King on the island of Grenada by a use of the royal prerogative was invalid.

Mansfield held that the King could use the prerogative to pass laws for a conquered colony such as Grenada (recently acquired from the French), but only up to the point that the King granted a right to a representative assembly. Once the inhabitants of a colony had an assembly, the King could no longer use the prerogative to legislate for the colony.

In this case, the King created the tax under his prerogative after he had granted a right to an assembly for Grenada, and therefore the prerogative tax was invalid.