The 1st United States Congress, comprising the United States Senate and the United States House of Representatives, met from March 4, 1789, to March 4, 1791, during the first two years of George Washington's presidency, first at Federal Hall in New York City and later at Congress Hall in Philadelphia. With the initial meeting of the First Congress, the United States federal government officially began operations under the new frame of government established by the 1787 Constitution. The apportionment of seats in the House of Representatives was based on the provisions of Article I, Section 2, Clause 3, of the Constitution. Both chambers had a Pro-Administration majority. Twelve articles of amendment to the Constitution were passed by this Congress and sent to the states for ratification; the ten ratified as additions to the Constitution on December 15, 1791, are collectively known as the Bill of Rights, with an additional amendment ratified more than two centuries later to become the Twenty-seventh Amendment to the United States Constitution.

The United States Senate is the upper chamber of the United States Congress. The United States Senate and the lower chamber of Congress, the United States House of Representatives, comprise the federal bicameral legislature of the United States. Together, the Senate and the House maintain authority under Article One of the U.S. Constitution to pass or defeat federal legislation. The Senate has exclusive power to confirm U.S. presidential appointments, approve or reject treaties, and try cases of impeachment brought by the House. The Senate and the House provide a check and balance on the powers of the executive and judicial branches of government.