The Federalist Party was a conservative and nationalist American political party and the first political party in the United States. It dominated the national government under Alexander Hamilton from 1789 to 1801. The party was defeated by the Democratic-Republican Party in 1800, and it became a minority party while keeping its stronghold in New England. It made a brief resurgence by opposing the War of 1812, then collapsed with its last presidential candidate in 1816. Remnants lasted for a few years afterwards.

The party appealed to businesses who favored banks, national over state government, and maintaining an army and navy. In world affairs, the party preferred Great Britain and strongly opposed involvement in the French Revolutionary and Napoleonic Wars. The party favored centralization, federalism, modernization, industrialization, and protectionism.

The Federalists called for a strong national government that promoted economic growth and fostered friendly relationships with Great Britain in opposition to Revolutionary France. The Federalist Party came into being between 1789 and 1790 as a national coalition of bankers and businessmen in support of Hamilton's fiscal policies. These supporters worked in every state to build an organized party committed to a fiscally sound and nationalistic government. The only Federalist president was John Adams. George Washington was broadly sympathetic to the Federalist program, but he remained officially non-partisan during his entire presidency. The Federalist Party controlled the national government until 1801, when it was overwhelmed by the Democratic-Republican opposition led by President Thomas Jefferson.

Federalist policies called for a national bank, tariffs, and good relations with Great Britain as expressed in the Jay Treaty negotiated in 1794. Hamilton developed the concept of implied powers and successfully argued the adoption of that interpretation of the Constitution. The Democratic-Republicans led by Jefferson denounced most of the Federalist policies, especially the bank and implied powers, and vehemently attacked the Jay Treaty as a sell-out of American interests to Britain. The Jay Treaty passed and the Federalists won most of the major legislative battles in the 1790s. They held a strong base in the nation's cities and in New England. They factionalized when President Adams secured peace with France, to the anger of Hamilton's larger faction. The Jeffersonians won the presidential election of 1800, and the Federalists never returned to power. They recovered some strength through their intense opposition to the War of 1812, but they practically vanished during the Era of Good Feelings that followed the end of the war in 1815.

The Federalists left a lasting legacy in the form of a strong federal government. After losing executive power, they decisively shaped Supreme Court policy for another three decades through Chief Justice John Marshall.

The term "Federalist" was previously used to refer to a somewhat different coalition of nationalists led by Washington, which advocated replacing the weaker national government under the Articles of Confederation with a new Constitution in 1789. This early coalition included Hamilton and James Madison.

The Federalists of this time were rivaled by the Anti-Federalists, who opposed the ratification of the Constitution and objected to creating a stronger central government. The critiques of the Constitution raised by the Anti-Federalists influenced the creation of the Bill of Rights. Federalists responded to these objections by promising to add a bill of rights as amendments to the Constitution to satisfy these concerns, which aided in securing acceptance and ratification of the Constitution by the states. The new United States Congress, initially with a Federalist majority, submitted to the states a series of amendments to guarantee specific freedoms and rights; once ratified, these would become the first ten amendments to the Constitution.

Upon taking office in 1789, President Washington nominated his wartime chief of staff Alexander Hamilton to the new office of Secretary of the Treasury. Hamilton wanted a strong national government with financial credibility, and he proposed the ambitious Hamiltonian economic program that involved the assumption of the state debts incurred during the American Revolution. This created a national debt and the means to pay it off, and it set up a national bank along with tariffs, with James Madison playing major roles in the program. Parties were considered to be divisive and harmful to republicanism, and no similar parties existed anywhere in the world.