In 1784, by an almost unanimous vote of the Legislature, Mr. King was sent a delegate to the old Congress, sitting at Trenton, and again in 1785 and 1786. In this body, in 1785, he moved "that there should be neither slavery nor involuntary servitude in any of the states described in the resolution of Congress in April, 1784, otherwise than in punishment of crime whereof the party shall have been personally guilty; and that this regulation shall be made an article of compact, and remain a fundamental principle of the constitution between the original states and each of the states named in the said resolve." Though this was not at the time acted upon, the principle was finally adopted almost word for word in the famous ordinance of 1787 for the government of the Northwestern Territory, a provision which had been prepared by Mr. King, and which was introduced into Congress by Nathan Dane, his colleague, while Mr. King was engaged in Philadelphia as a member from Massachusetts of the convention to form a constitution for the United States.

He was also appointed by his state to the commissions to settle the boundaries between Massachusetts and New York, and to convey to the United States lands lying west of the Alleghenies. While in Congress in 1786 he was sent with James Monroe to urge upon the Legislature of Pennsylvania the payment of the 5% impost, but was not so successful as he had been in Massachusetts. In 1787 Mr. King was appointed one of the delegates from his state to the convention at Philadelphia to establish a more stable government for the United States. In this body he bore a conspicuous and able part. He was one of the members to whom was assigned the duty of making a final draft of the Constitution of the United States. When the question of its adoption was submitted to the states, Mr. King was sent to the Massachusetts Convention, and, although the opposition to it was carried on by most of the chief men of the state, his familiarity with its provisions, his clear explanation of them, and his earnest and eloquent statement of its advantages, contributed greatly to bring about its final adoption.

Mr. King had now given up the practice of law, and having in 1786 married Mary, the daughter of John Alsop, a deputy from New York to the first Continental Congress, he took up his residence in New York in 1788. The next year he was elected to the assembly of the state, and while serving in that body, received the unexampled welcome of an immediate election with Schuyler to the Senate" of the United States. In this body he was rarely absent from his seat, and did much to put the new government into successful operation. One of the grave questions that arose was that of the ratification of the Jay Treaty with Great Britain in 1794. Of this he was an earnest advocate, and when he and his friend General Hamilton were prevented from explaining its provisions to the people in public meeting in New York, they united in publishing, under the signature of "Camillus," a series of explanatory papers, of which those relating to commercial affairs and maritime law were written by Mr. King. This careful study laid the foundation of much of the readiness and ability that he manifested during his residence in England as United States Minister, to which post, while serving his second term in the Senate, he was appointed by General Washington in 1796, and in which he continued during the administration of John Adams and two years of that of Thomas Jefferson.

The contingencies arising from the complicated condition of affairs, political and commercial, between Great Britain and her continental neighbors, required careful handling in looking after the interests of his country: and Mr. King, by his firm and intelligent presentation of the matters entrusted to him, did good service to his country and assisted largely to raise it to consideration and respect. In 1803 he was relieved, at his own request, from his office, and, returning to this country, removed to Jamaica, L.I. There, in the quiet of a country life, he interested himself in agriculture, kept up an extensive correspondence with eminent men at home and abroad, and enriched his mind by careful and varied reading. He was opposed on principle to the War of 1812 with England, when it was finally declared, but afterward gave to the government his support, both by money and by his voice in private and in the United States Senate, to which he was again elected in 1813.

In 1814 he made an eloquent appeal against the proposed desertion of Washington after the British had burned the Capitol. In 1816, without his knowledge, he was nominated as Governor of New York, but was defeated, as he was also when a candidate of the Federal Party for the presidency against James Monroe. During this senatorial term he opposed the establishment of a national bank with $50,000,000 capital; and, while resisting the efforts of Great Britain to exclude the United States from the commerce of the West Indies, contributed to bring about the passage of the navigation act of 1818. The disposal of the public lands by sales on credit was found to be fraught with much danger. Mr. King was urgent in calling attention to this, and introduced and carried a bill directing that they should be sold for cash, at a lower price, and under other salutary restrictions.

In 1819 he was again elected to the Senate by a Legislature that was opposed to him in politics as before. Mr. King resisted the admission of Missouri with slavery, and his speech on that occasion, though only briefly reported, contained this carefully prepared statement:

" Mr. President, I approach a very delicate subject. I regret the occasion that renders it necessary for me to speak of it, because it may give offence where none is intended. But my purpose is fixed. Mr. President, I have yet to learn that one man can make a slave of another. If one man cannot do so, no number of individuals can have any better right to do it. And I hold that all laws or compacts imposing any such condition upon any human being are absolutely void, because contrary to the law of nature, which is the law of God, by which he makes his ways known to man, and is paramount to all human control."

He was equally opposed to the compromise offered by Mr. Clay on principle, and because it contained the seeds of future troubles. Upon the close of this senatorial term he put upon record, in the senate, a resolution which he fondly hoped might provide a way for the final extinction of slavery. It was to the effect that, whenever that part of the public debt for which the public lands were pledged should have been paid, the proceeds of all future sales should be held as a fund to be used to aid the emancipation of such slaves, and the removal of them and of free persons of color, as by the laws of the states might be allowed to any territory beyond the States. His purpose to retire to private life was thwarted by an urgent invitation from John Quincy Adams, in 1825, to accept the mission to Great Britain. Mr. King reluctantly acquiesced and sailed for England, where he was cordially received, but after a few months he was obliged, through failing health, to return home.

--His wife, Mary King, born in New York, 17 October 1769; died in Jamaica, New York, 5 June 1819, was the only daughter of John Alsop, a merchant, and a member of the Continental Congress from New York, and married Mr. King in New York on 30 March 1786, he being at that time a delegate from Massachusetts to the Congress then sitting in that city. Mrs. King was a lady of remarkable beauty, gentle and gracious manners, and well cultivated mind, and adorned the high station, both in England and at home, that her husband's official positions and their own social relations entitled them to occupy. The latter years of her life, except while in Washington, were passed in Jamaica, Long Island .