Along with Baker v. Carr (1962) and Wesberry v. Sanders (1964), it was part of a series of Warren Court cases that applied the principle of "one person, one vote" to U.S. legislative bodies.

In a majority opinion joined by five other justices, Chief Justice Earl Warren ruled that the Fourteenth Amendment's Equal Protection Clause requires states to establish state legislative electoral districts roughly equal in population.

In his dissenting opinion, Associate Justice John Marshall Harlan II argued that the Equal Protection Clause was not designed to apply to voting rights.

And the right of suffrage can be denied by a debasement or dilution of the weight of a citizen's vote just as effectively as by wholly prohibiting the free exercise of the franchise.

The eight justices who struck down state senate inequality based their decision on the principle of "one person, one vote."

In his majority decision, Chief Justice Earl Warren said "Legislators represent people, not trees or acres.

In dissent, Justice John Marshall Harlan II wrote that the majority had chosen to ignore the language, history, and original intent of the Equal Protection Clause, which did not extend to voting rights.

The Court had already extended "one person, one vote" to all U.S. congressional districts in Wesberry v. Sanders (1964) a month before, but not to the Senate.

[11] He warned that: [T]he forces of our national life are not brought to bear on public questions solely in proportion to the weight of numbers.