Answer:
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.
He was one of many delegates to attend the Constitutional Convention in Philadelphia in 1787 and used his platform to help shape the document as best he could. When the ratification process stalled, he worked hard to bring uncertain Anti-Federalists onto his side. His success helped give the new Federalist Party some short-lived success.