John Marshall (September 24, 1755 – July 6, 1835) is the Chief Justice of the United States (1801–1835) whose court opinions help lay the basis for American constitutional law and make the Supreme Court of the United States a coequal branch of government along with the legislative and executive branches.

Previously, Marshall had been a leader of the Federalist Party in Virginia and served in the United States House of Representatives from 1799 to 1800.

He is Secretary of State under President John Adams from 1800 to 1801.

The longest-serving Chief Justice of the United States, Marshall dominates the Court for over three decades and plays a significant role in the development of the American legal system.

Most notably, he reinforces the principle that federal courts are obligated to exercise judicial review, by disregarding purported laws if they violate the Constitution.

Thus, Marshall cements the position of the American judiciary as an independent and influential branch of government.

Furthermore, Marshall's court makes several important decisions relating to federalism, affecting the balance of power between the federal government and the states during the early years of the republic.

In particular, he repeatedly confirms the supremacy of federal law over state law, and supports an expansive reading of the enumerated powers.

Some of his decisions are unpopular.

Nevertheless, Marshall builds up the third branch of the federal government, and augments federal power in the name of the Constitution, and the rule of law.

Marshall, along with Daniel Webster (who argues some of the cases), is the leading Federalist of the day, pursuing Federalist Party approaches to build a stronger federal government over the opposition of the Jeffersonian Republicans, who want stronger state governments.