The US Supreme Court has ruled that same-sex marriage is a legal right across the United States.
People celebrate in front of the US Supreme Court after the ruling in favor of same-sex marriage. Photo: AFP
It means the 14 states with bans on same-sex marriage will no longer be able to enforce them.
Justice Anthony Kennedy wrote that the plaintiffs asked "for equal dignity in the eyes of the law. The Constitution grants them that right."
The ruling brings to an end more than a decade of bitter legal battles.
Same-sex couples in several affected states including Georgia, Michigan, Ohio and Texas rushed to wed on Friday.
However officials in some states including Mississippi and Louisiana said marriages had to wait until procedural issues were addressed.
President Barack Obama said the ruling was a "victory for America".
"When all Americans are treated as equal, we are all more free," he said.
However, Christian conservatives decried the decision.
Former Arkansas governor and presidential candidate Mike Huckabee called the ruling "an out-of-control act of unconstitutional, judicial tyranny".
And Kellie Fiedorek, a lawyer for an anti-gay marriage advocacy group, said the decision "ignored the voices of thousands of Americans".
Minutes after the ruling, couples in one of the states that had a ban, Georgia, lined up in hope of being wed.
On social media, Democratic presidential candidate Hillary Clinton merely tweeted the word "proud" and the White House changed its Twitter avatar into the rainbow colours.
The case considered by the court concerned Jim Obergefell, an Ohio resident who was not recognised as the legal widower of his late husband, John Arthur.
"It's my hope that gay marriage will soon be a thing of the past, and from this day forward it will simply be 'marriage,'" an emotional Mr Obergefell said outside the court.
People celebrate inside the Stonewall Inn, an iconic gay bar recently granted historic landmark status in New York's West Village. Photo: AFP
The first state to allow same-sex marriage was Massachusetts, which granted the right in 2004.
In recent years, a wave of legal rulings and a dramatic shift in public opinion have expanded gay marriage in the US.
In 2012, the high court struck down a federal anti same-sex marriage law.