John Marshall (September 24, 1755 – July 6, 1835) was an American politician and lawyer who served as the fourth chief justice of the United States from 1801 until his death in 1835. Marshall remains the longest-serving chief justice and fourth-longest serving justice in Supreme Court history, and he is widely regarded as one of the most influential justices to ever sit on the Supreme Court. Prior to joining the Supreme Court (and for one month simultaneous to his tenure as Chief Justice), Marshall served as the fourth United States Secretary of State under President John Adams.

Marshall was born in Germantown in the Colony of Virginia in 1755. After the outbreak of the American Revolutionary War, he joined the Continental Army, serving in numerous battles. During the later stages of the war, he was admitted to the state bar and won election to the Virginia House of Delegates. Marshall favored the ratification of the United States Constitution, and he played a major role in Virginia's ratification of that document. At the request of President Adams, Marshall traveled to France in 1797 to help bring an end to attacks on American shipping. In what became known as the XYZ Affair, the government of France refused to open negotiations unless the United States agreed to pay bribes. After returning to the United States, Marshall won election to the United States House of Representatives and emerged as a leader of the Federalist Party in Congress. He was appointed secretary of state in 1800 after a cabinet shake-up, becoming an important figure in the Adams administration.

In 1801, Adams appointed Marshall to the Supreme Court. Marshall quickly emerged as the key figure on the court, due in large part to his personal influence with the other justices. Under his leadership, the court moved away from seriatim opinions, instead issuing a single majority opinion that elucidated a clear rule. The 1803 case of Marbury v. Madison presented the first major case heard by the Marshall Court. In his opinion for the court, Marshall upheld the principle of judicial review, whereby courts could strike down federal and state laws if they conflicted with the Constitution. Marshall's holding avoided direct conflict with the executive branch, which was led by Democratic-Republican President Thomas Jefferson. By establishing the principle of judicial review while avoiding an inter-branch confrontation, Marshall helped implement the principle of separation of powers and cement the position of the American judiciary as an independent and co-equal branch of government.

After 1803, many of the major decisions issued by the Marshall Court confirmed the supremacy of the federal government and the federal Constitution over the states. In Fletcher v. Peck and Dartmouth College v. Woodward, the court invalidated state actions because they violated the Contract Clause. The court's decision in McCulloch v. Maryland upheld the constitutionality of the Second Bank of the United States and established the principle that the states could not tax federal institutions. The cases of Martin v. Hunter's Lessee and Cohens v. Virginia established that the Supreme Court could hear appeals from state courts in both civil and criminal matters. Marshall's opinion in Gibbons v. Ogden established that the Commerce Clause bars states from restricting navigation. In the case of Worcester v. Georgia, Marshall held that the Georgia criminal statute that prohibited non-Native Americans from being present on Native American lands without a license from the state was unconstitutional. Marshall died in 1835, and Andrew Jackson appointed Roger Taney as his successor.