Article One of the United States Constitution requires U.S. House districts to be apportioned by population among the states, but it did not explicitly require states to establish districts equal in population. The case arose from a challenge to the unequal population of congressional districts in the state of Georgia.
In his majority opinion, which was joined by five other justices, Associate Justice Hugo Black held that the text of the Article One required that "as nearly as practicable one man's vote in a congressional election is to be worth as much as another's." The decision had a major impact on representation in the House, as many states had districts of unequal population, often to the detriment of urban voters. The United States Senate was unaffected by the decision since the Constitution explicitly grants each state two senators.
Writing for the Court majority in Wesberry, Justice Black argued that a reading of the debates of the Constitutional Convention demonstrated conclusively that the Framers had meant, in using the phrase “by the People,” to guarantee equality of representation in the election of Members of the House of Representatives.
Writing in dissent, Justice Harlan argued that the statements cited by Justice Black had uniformly been in the context of the Great Compromise. Justice Harlan further argued that the Convention debates were clear to the effect that Article I, § 4, had vested exclusive control over state districting practices in Congress and that the Court action overrode a congressional decision not to require equally populated districts.