In Marbury v. Madison, the U.S. Supreme Court held that a court can declare an act of Congress void when it conflicts with the Constitution, according to the Legal Information Institute. The decision makes the Court the final arbiter of the constitutionality of congressional legislation.
The events leading up to the case began in 1801, when Federalist William Marbury was appointed as a justice of the peace for the District of Columbia in the closing days of John Adams' presidency, notes History.com. Secretary of State James Madison refused to approve the commission, as well as the commissions of three other appointees. Collectively, the denied parties sued to compel finalization of the commissions by petitioning the Supreme Court for a writ of mandamus.
The Supreme Court was tasked with resolving whether the petitioners were entitled to their appointments, and whether it was the appropriate place to obtain relief, explains Oyez. The Court unanimously denied the petition and refused to issue the writ, noting that nothing in the Constitution gives them the authority to issue writs of mandamus. Citing Section 13 of the Judiciary Act of 1789, the Court noted that while such writs might be issued, that particular section of the act was invalid as being inconsistent with the Constitution. In spite of its reasoning, the Court concluded that the petitioners were nevertheless entitled to their commissions. The case confirmed the principle that legislative acts that conflict with the Constitution are invalid, thus establishing the Supreme Court's power of judicial review.