On June 26, 2008, by a 5 to 4 decision, the Supreme Court upheld the federal appeals court ruling, striking down the D.C. gun law. Justice Antonin Scalia, writing for the majority, stated, "In sum, we hold that the District's ban on handgun possession in the home violates the Second Amendment, as does its prohibition against rendering any lawful firearm in the home operable for the purpose of immediate self-defense ... We affirm the judgment of the Court of Appeals.” This ruling upholds the first federal appeals court ruling ever to void a law on Second Amendment grounds.

The Court based its reasoning on the grounds:

• that the operative clause of the Second Amendment—"the right of the people to keep and bear Arms, shall not be infringed"—is controlling and refers to a pre-existing right of individuals to possess and carry personal weapons for self-defense and intrinsically for defense against tyranny, based on the bare meaning of the words, the usage of "the people" elsewhere in the Constitution, and historical materials on the clause's original public meaning;
• that the prefatory clause, which announces a purpose of a "well regulated Militia, being necessary to the security of a free State", comports with the meaning of the operative clause and refers to a well-trained citizen militia, which "comprised all males physically capable of acting in concert for the common defense", as being necessary to the security of a free polity;
• that historical materials support this interpretation, including "analogous arms-bearing rights in state constitutions" at the time, the drafting history of the Second Amendment, and interpretation of the Second Amendment "by scholars, courts, and legislators" through the late nineteenth century; and
• that none of the Supreme Court's precedents forecloses the Court's interpretation, specifically United States v. Cruikshank (1875), Presser v. Illinois (1886), nor United States v. Miller (1939).

However, "[l]ike most rights, the Second Amendment is not unlimited. It is not a right to keep and carry any weapon whatsoever in any manner whatsoever and for whatever purpose." The Court's opinion, although refraining to undertake an exhaustive analysis of the full scope of the right, "should not be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms."

Therefore, the District of Columbia's handgun ban is unconstitutional, as it "amounts to a prohibition on an entire class of 'arms' that Americans overwhelmingly choose for the lawful purpose of self-defense". Similarly, the requirement that any firearm in the home be disassembled or bound by a trigger lock is unconstitutional, as it "makes it impossible for citizens to use arms for the core lawful purpose of self-defense".