The Supreme Court has ruled 5-4 to strike down the Defense of Marriage Act as unconstitutional in a major victory for advocates of gay marriage and a blow to House Republican leaders. California’s Proposition 8 banning gay marriage also fell, with the court ruling that the appellants did not have standing to appeal a lower court decision overturning the law.

House Republicans authorized spending up to $3 million to defend DOMA in court after President Barack Obama’s administration refused to do so, over the protests of Democrats. But the court ruled that the law violated the equal protection guarantees in the Constitution.

“DOMA instructs all federal officials, and indeed all persons with whom same-sex couples interact, including their own children, that their marriage is less worthy than the marriages of others,” the court found. “The federal statute is invalid, for no legitimate purpose overcomes the purpose and effect to disparage and to injure those whom the State, by its marriage laws, sought to protect in personhood and dignity.

“By seeking to displace this protection and treating those persons as living in marriages less respected than others, the federal statute is in violation of the Fifth Amendment.”

The decision, written by Justice Anthony M. Kennedy joined by the liberal wing of the court, isn’t likely to lead to any immediate congressional action; Obama’s administration had dropped its defense of DOMA and the president came out for gay marriage last year. A parade of lawmakers have come out in recent months in support of gay marriage as the court took up the case, with 54 members of the Senate now in support, including three Republicans.

Indeed, Chief Justice John G. Roberts Jr. had nodded during the oral arguments to the shifting politics on the issue.

“As far as I can tell, political figures are falling over themselves to endorse your side of the case,” he told one of the plaintiffs’ lawyers.

Speaker John A. Boehner, R-Ohio, issued a short statement after the decision.

“The House intervened in this case because the constitutionality of a law should be judged by the Court, not by the president unilaterally,” Boehner said. “While I am obviously disappointed in the ruling, it is always critical that we protect our system of checks and balances. A robust national debate over marriage will continue in the public square, and it is my hope that states will define marriage as the union between one man and one woman.”

The decision does, meanwhile, have an impact on the immigration debate. An amendment granting partners of gay couples equal treatment in immigration has been a heated debate in the Senate; now, married gay couples will be treated the same.

Senate Democratic leaders and the White House are also pushing to expand gay rights further with votes on the Employment Non-Discrimination Act banning workplace discrimination.

Republicans in recent years — as polls have moved sharply in favor of gay rights — have ratcheted back on anti-gay-rights media events and press releases relative to the middle of the last decade, when the GOP used gay marriage as a wedge issue and President George W. Bush sought to define marriage in the Constitution as a union between one man and one woman.