Yes. Not only was Hamilton a Federalist, but he was also one of the most significant figures in creating the Federalist Party and championing some of the federalist ideals for the US Constitution.

Hamilton's views became the basis for the Federalist Party, which was opposed by the Democratic-Republican Party led by Thomas Jefferson. Hamilton and other Federalists supported the Haitian Revolution, and Hamilton helped draft the constitution of Haiti.

Since the Caesar letters seemed not influential, Hamilton turned to another classical pseudonym, Publius, and to two collaborators, James Madison, the delegate from Virginia, and John Jay, the secretary of foreign affairs, to write The Federalist, a series of 85 essays in defense of the Constitution and republican government that appeared in newspapers between October 1787 and May 1788.

Along with James Madison and John Jay, Hamilton published a series of 85 essays defending the new document to the American people. Hamilton wrote no fewer than 51 of these Federalist Papers, and they would become his best-known writings.