The Senate of the United States shall be composed of two Senators from each State, chosen by the Legislature thereof, for six Years. [U.S. Constitution, Article I, section 3, clause 1]
The Virginia Plan, which set the initial terms of debate for the Constitutional Convention, did not specify a length of term for either house of Congress. It merely proposed that members of the Senate “hold their offices for a term sufficient to ensure their independency.”
In deciding term lengths, Convention delegates turned to the practices of state governments. Although the majority of states set one-year terms for both houses of their legislatures, five state constitutions established longer terms for upper house members. South Carolina’s senators served two-year terms, for example, while senators in Delaware served three-year terms with one-third of the senate’s nine members up for reelection each year. New York and Virginia implemented a similar system but with four-year terms instead of three. Only Maryland’s senate, whose members were not directly elected by the people, featured five-year terms.
The first proposal, from Virginians Edmund Randolph and James Madison, called for seven-year Senate terms. Citing Maryland’s system, Randolph and Madison argued that a long term would create stability in the Senate and provide an effective check on the more democratic House of Representatives. George Read of Delaware proposed an even longer term of nine years. Madison endorsed this long term, arguing it would contribute to the “wisdom and virtue” required for the body to counter “symptoms of a levelling spirit” among the people. A few delegates, such as New York’s Alexander Hamilton, suggested that senators be granted life tenure, as existed in England’s House of Lords. Hamilton contended this was necessary to protect senators against the "amazing violence and turbulence of the democratic spirit,” but few delegates supported this idea.
While some delegates proposed long terms to allow for an independent Senate, others worried that long terms would create too much independence. Charles Cotesworth Pinckney of South Carolina, for example, suggested that longer terms would lead senators to lose sight of their state’s interest. Connecticut’s Roger Sherman preferred four-year terms, arguing that frequent elections “preserve the good behavior of rulers.”
On June 26, with a 7 to 4 vote, the delegates compromised and adopted six-year terms for the Senate. In Federalist No. 62, James Madison defended six-year terms for senators, insisting that six-year terms would have a stabilizing effect on the new national government. Long terms, he argued, would reduce turnover in the legislature, allow senators to take responsibility for measures over time, and make senators largely independent of public opinion.