WASHINGTON — A deeply divided Supreme Court on Friday delivered a historic victory for gay rights, ruling 5-4 that the Constitution requires that same-sex couples be allowed to marry no matter where they live.

The court's action rewarded years of legal work by advocates of same-sex marriage and marked the culmination of an unprecedented upheaval in public opinion and the nation's jurisprudence.

Justice Anthony Kennedy, who has written all of the court's decisions recognizing and expanding gay rights, said the decision was based on the fundamental right to marry and the equality that must be afforded gay Americans.

"Under the Constitution, same-sex couples seek in marriage the same legal treatment as opposite-sex couples, and it would disparage their choices and diminish their personhood to deny them this right," Kennedy wrote.

He was joined in the ruling by the court's liberal justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan.

RULING: Read the full Supreme Court ruling on Obergefell v. Hodges

All four of the court's most conservative members — Chief Justice John Roberts and Justices Antonin Scalia, Clarence Thomas and Samuel Alito — dissented, and each wrote a separate opinion.

The common theme in their dissents was that judicial activism on the part of five members of the court had usurped a power that belongs to the people.

Reading a dissent from the bench for the first time in his tenure, Roberts said, "Just who do we think we are? I have no choice but to dissent."

In his opinion, Roberts wrote: "Many people will rejoice at this decision, and I begrudge none their celebration. But for those who believe in a government of laws, not of men, the majority's approach is deeply disheartening."

Scalia called the decision a "threat to American democracy," saying it was "constitutional revision by an unelected committee of nine."

In a statement in the White House Rose Garden, President Barack Obama hailed the decision: " Today we can say in no uncertain terms that we have made our union a little more perfect."

There were wild scenes of celebrations on the sidewalk outside the Supreme Court, as same-sex marriage supporters had arrived early, armed with signs and rainbow flags. They celebrated the announcement of a constitutional right to something that did not legally exist anywhere in the world until the turn of the new century.

The celebration continued into the night, and a crowd gathered outside the White House, its north side illuminated in rainbow colors. Other landmarks across the U.S. — including Niagara Falls, the Empire State Building, Disney's Cinderella's Castle and Denver's City and County Building — were illuminated similarly.

Jim Obergefell — who became the face of the case, Obergefell vs. Hodges, when he sought to put his name on his husband's death certificate as the surviving spouse — said: "Today's ruling from the Supreme Court affirms what millions across the country already know to be true in our hearts: that our love is equal.

"It is my hope that the term 'gay marriage' will soon be a thing of the past, that from this day forward it will be simply 'marriage.' All Americans deserve equal dignity, respect and treatment when it comes to the recognition of our relationships and families."

PHOTOS: Nation reacts to Supreme Court ruling legalizing same-sex marriage

But Austin Nimocks, senior counsel for the Alliance Defending Freedom, a group of traditional-marriage advocates, said: "Today, five lawyers took away the voices of more than 300 million Americans to continue to debate the most important social institution in the history of the world. ... Nobody has the right to say that a mom or a woman or a dad or a man is irrelevant. There are differences that should be celebrated. Millions of Americans still believe that."

Supreme Court Ruling Approves Same-Sex Marriage

This country's first legally recognized same-sex marriages took place just 11 years ago, the result of a Massachusetts state Supreme Court decision.

Now, more than 70 percent of Americans live in states where same-sex couples are allowed to marry, according to estimates.

The U.S. Supreme Court used cases from Michigan, Ohio, Kentucky and Tennessee — where restrictions about same-sex marriage were upheld by an appeals court last year — to find that the Constitution does not allow such prohibitions.

Kennedy has written the Supreme Court's most important gay rights cases: overturning criminal laws on homosexual conduct, protecting gays from discrimination and declaring that the federal government could not refuse to recognize same-sex marriages performed where they were legal.

He often employs a lofty, writing-for-history tone, and Friday's decision was no different.

INTERACTIVE: Examine a map and timeline detailing same-sex marriage's spread across the country

Referring to the couples who brought the cases before the court, Kennedy wrote: "It would misunderstand these men and women to say they disrespect the idea of marriage. Their plea is that they do respect it, respect it so deeply that they seek to find its fulfillment for themselves. Their hope is not to be condemned to live in loneliness, excluded from one of civilization's oldest institutions."

Kennedy did not respond directly to the court's dissenters, but he addressed the argument that the court was creating a new constitutional right.

The right to marriage is fundamental, he said. The difference is society's way of thinking who may marry, he said.

"The limitation of marriage to opposite-sex couples may long have seemed natural and just, but its inconsistency with the central meaning of the fundamental right to marry is now manifest," he wrote. "With that knowledge must come the recognition that laws excluding same-sex couples from the marriage right impose stigma and injury of the kind prohibited by our basic charter."

Scalia declared that Kennedy's writing style was "as pretentious as its content is egotistic."

And Roberts, in a biting dissent, said the decision was "an act of will, not legal judgment," with "no basis in the Constitution or this court's precedent."

He added: "The court invalidates the marriage laws of more than half the states and orders the transformation of a social institution that has formed the basis of human society for millennia, for the Kalahari Bushmen and the Han Chinese, the Carthaginians and the Aztecs. Just who do we think we are?"

The questions raised in the cases decided Friday were left unanswered in 2013, when the justices last confronted the issue of same-sex marriage. A slim majority of the court said at the time that a key portion of the Defense of Marriage Act — withholding the federal government's recognition of same-sex marriages — was unconstitutional. In a separate case, the court said procedural issues kept it from answering the constitutional question in a case from California, but that move allowed same-sex marriages to resume in that state.

Since then, courts across the nation — with the notable exception of the Cincinnati-based federal appeals court that left intact the restrictions in the four states at issue — have struck down a string of state prohibitions on same-sex marriage, many of them passed by voters.

When the Supreme Court declined to review a clutch of those court decisions in October, same-sex marriage proliferated across the country. The number of states required to allow gay marriages grew dramatically, offering the kind of cultural shift the court often likes to see before approving a fundamental change.

Public attitudes toward such unions have undergone a remarkable change as well. A recent poll showed a record 61 percent of Americans say they support same-sex marriage. The acceptance is driven by higher margins among the young.

The Obama administration had urged the court to find that the Constitution requires that such restrictions be struck down, and Solicitor General Donald Verrilli made the case on behalf of the administration at the court's oral arguments in April.