On June 26, 2015, the U.S. Supreme Court ruled 5 to 4 in Obergefell v. Hodges that same-sex couples have a constitutional right to marry in all fifty states. Writing for the majority, Justice Anthony Kennedy declared that the Fourteenth Amendment's guarantees of liberty and equal protection extend to same-sex marriage, striking down state bans that had persisted in thirteen states. The decision represented the culmination of decades of legal advocacy and marked a watershed moment in American civil rights history.

The case consolidated four separate challenges from Michigan, Ohio, Kentucky, and Tennessee, where same-sex couples and their surviving partners had been denied marriage licenses or recognition of out-of-state marriages. The plaintiffs, represented by lawyers including Theodore Olson and David Boies, argued that denial of marriage licenses violated fundamental constitutional protections. Opponents contended that marriage had traditionally been defined as between a man and a woman, and that states retained the authority to define it. Chief Justice John Roberts and Justices Clarence Thomas, Samuel Alito, and Antonin Scalia dissented, with Roberts warning the decision would have "consequences" for religious liberty.

The ruling dismantled the remaining legal barriers to same-sex marriage across the nation in a single stroke, overriding the Defense of Marriage Act's definition and invalidating state constitutional amendments that had defined marriage as heterosexual. Within days, county clerks nationwide began issuing marriage licenses to same-sex couples. The decision generated immediate celebrations at marriage equality rallies and also provoked substantial opposition from religious conservatives who raised concerns about religious freedom protections.

Obergefell fundamentally reshaped American law and social policy after decades of incremental progress. The 2003 Lawrence v. Texas decision had decriminalized same-sex conduct; Massachusetts legalized same-sex marriage in 2004; and by 2015, thirty-seven states plus the District of Columbia already permitted it. Yet the Supreme Court's decision ensured uniform protection nationwide, preventing a patchwork of state restrictions from persisting. The ruling demonstrated the Court's power of judicial review to strike down legislation conflicting with constitutional guarantees, extending those protections to a group that had faced systematic legal discrimination.