King’s early career included a term in the Massachusetts legislature and in Congress. In the Constitutional Convention in 1787, as a final step, a five-man committee, including Rufus King a Dartmouth graduate, was appointed to arrange the style of the document. King was also involved in the Dartmouth College Case over the controversy that arose about schools established under a Royal Charter.

Having moved to New York, King was elected a U. S. Senator from that state and served four terms. During the discussion over the Missouri Compromise in 1820, Senator King asserted that Congress was empowered to forbid slavery in Missouri and to make the prohibition of slavery a pre-requisite for admission as a state.

King was defeated for the vice-presidency in 1804 and 1808 and in his campaign for the presidency in 1816, rechartering of the United States Bank was a leading issue. He ran on the waning Federal party ticket and was badly defeated.