Which act was declared unconstitutional in Marbury vs. Madison?

The correct answer is that the Judiciary Act of 1801 was declared unconstitutional in the landmark case of Marbury v. Madison. This case, decided in 1803, is significant because it established the principle of judicial review, which allows the Supreme Court to invalidate laws that are in conflict with the Constitution.

The Judiciary Act of 1801 was criticized for its provisions that expanded the number of federal courts and judges, which the incoming administration of Thomas Jefferson viewed as an attempt by John Adams' administration to pack the judiciary with Federalist appointees. When William Marbury sought to compel the new Secretary of State, James Madison, to deliver his commission as a midnight judge, the Supreme Court, led by Chief Justice John Marshall, ruled that while Marbury had a right to his commission, the Court did not have the authority to issue a writ of mandamus based on the stipulations of the Judiciary Act of 1789, which conflicted with the Constitution. Thus, that specific part of the Act was found to be unconstitutional.

This case is foundational in U.S. legal history, as it affirmed the role of the judiciary in ensuring that laws align with the Constitution, demonstrating the balance of power among the branches of government.