James Madison arrived in Philadelphia once again on May 3, 1787, eager to get to work on the new American constitution. Over the past several months, he had boned up on the history and political philosophy of republican governments, paying particular attention to the writings of the French thinker Montesquieu. By the time the Constitutional Convention opened on May 25, he had a very clear picture of how he believed the government should be constituted. He expressed his view to George Washington in a letter to the general the month before, proposing a "radical" plan for a great federal republic, and referring to what he called the "supremacy of the national authority." Never before in history had there existed a republic of such a great size: even Montesquieu, Madison's guide in so many questions, doubted whether any sort of government besdides a monarchy could rule over such a vast geographical territory. Madison was convinced otherwise.
The members of the Virginia delegation gathered together before the opening of the Convention to draft a proposal for the constitution. Madison himself had already done much of the work, conceiving an American government composed of separate executive, legislative, and judicial powers, and one which was founded on the authority of the American people at large, not on the authority of the state governments. The executive power would be strong, the legislature would have two branches–an upper and a lower house–and the judicial power would serve the function of guarding the rule of law and the constitutional separation of powers.
The Virginia Plan, essentially Madison's brainchild, was presented to the general convention and adopted as the working model for debate on May 29. The debate was long and contentious. No extensive record of the arguments made throughout would have existed if it had not been for Madison's keeping a detailed journal of the proceedings. His presence was crucial at this convention, and he earned the respect of the other delegates. One of those delegates, William Pierce of Georgia, wrote that Madison was "a character who has long been in public life; and what is very remarkable every Person seems to acknowledge his greatness. He blends together the profound politician, with the Scholar. In the management of every great question he evidently took the lead in the Convention. [H]e always comes forward the best informed Man of any point in debate."
On September 17, 1787, the Constitutional Convention finished its work, and the proposed constitution was signed by all but three delegates present. The Virginians George Mason, and Edmund Randolph, and Massachusetts delegate Elbridge Gerry refused to sign, fearing the strong power it would wield over the states if adopted. Significantly, Madison himself was a bit disappointed in the final outcome, but his objection was that the government would be too weak, as the Convention had rejected his original idea that the Congress would have veto power over any state law. He was determined, however, to see the Constitution ratified by the states and become the law of the land.
Relocating to New York for the winter of 1787–1788, Madison joined forces with the prominent supporters of Federalism, Alexander Hamilton and John Jay, to write a total seventy-seven papers for the New York press in defense of the proposed Constitution. He wrote the papers under the pen-name Publius, and they were soon printed and distributed nationally under the title The Federalist. The arguments presented in the text were rigorous and convincing. Among Madison's many contributions was Federalist No. 10, which became a classic document in American political. Federalist No. 10, explained the nature of republican government and discussed factions and political parties.
In March 1788, Madison returned home to Virginia. He was worried that Virginia, under the influence of anti-Federalists George Mason and Patrick Henry, would not vote to ratify the Constitution. He was elected to the Virginia convention, which debated the matter shortly after his return home, and he worked for the Constitution's acceptance. On June 25, the convention approved the Constitution by a vote of eighty-nine for; seventy-nine against. This vote was not necessary for making the Constitution the law of the land, as nine states, the number required for its ratification, had already signed onto the Constitution. Virginia's support was crucial, however, for the stability of the new nation.