In 1787, Morris was selected as a delegate to the Philadelphia Convention, which wrote and proposed a new constitution for the United States. Morris rarely spoke during the convention, but the constitution produced by the convention reflected many of his ideas. Morris and his allies helped ensure that Pennsylvania ratified the new constitution, and the document was ratified by the requisite number of states by the end of 1788. The Pennsylvania legislature subsequently elected Morris as one of its two inaugural representatives in the United States Senate. Morris declined Washington's offer to serve as the nation's first Treasury Secretary, instead suggesting Alexander Hamilton for the position. In the Senate, Morris supported Hamilton's economic program and aligned with the Federalist Party. During and after his service in the Senate, Morris went deeply into debt speculating on land leading into the Panic of 1796–97. Unable to pay his creditors, he was confined in the Prune Street debtors' apartment adjacent to Walnut Street Prison from 1798 to 1801. After being released from prison, he lived a quiet, private life in a modest home in Philadelphia until his death in 1806.