SAN FRANCISCO – Hours before the California Supreme Court issued its decision on gay marriage, Mayor Gavin Newsom heard rumblings that the justices would uphold the state's ban.

He prepared for defeat, knowing his stance on the issue often has been a lonely one since he opened San Francisco City Hall's doors in 2004 to a same-sex wedding spree, a move that set the stage for Thursday's historic ruling. The same court had ordered him to stop the nuptials.

So when word came in that the justices had overturned the ban, Newsom sat at his desk, surrounded by his closest aides, looking stunned. The mayor was elated – and vindicated.

Immediately City Hall staffers' cell phones lit up with a text messages declaring, “We Won!” and cheers and applause filled the mayor's office.

“It was an exhilarating feeling, that's the best I can describe it,” Newsom said after confirming the justices' ruling with the city attorney.

For Newsom, the ruling was a personal and political triumph on an issue that has come to define him on the national stage. And the timing couldn't be more ideal, as he explores a run for governor or a spot in Congress.

Newsom's actions on Feb. 12, 2004, made headlines around the world, when he issued the city's first gay marriage license to lesbian activists Del Martin and Phyllis Lyon, who had been together 51 years at the time. Newsom's decision to flout state law drew criticism, and not just from conservatives.

“The danger before was that he was principled but out of the mainstream, because not many Democratic candidates shared the same view,” said University of California, Berkeley political scientist Bruce Cain.

The rookie mayor, just one month into the job, even got heat from longtime allies, including Dianne Feinstein. The senior California senator said the intense focus on same-sex marriage during a presidential election year contributed to the party's defeat.

Newsom would forever be linked to the image of more than 4,000 same-sex couples exchanging vows at City Hall, a link that threatened to doom his aspirations for higher office.

But he swiped those concerns aside, arguing that same-sex marriage was a fundamental issue of civil rights. The city eventually joined other groups in suing California for violating the state constitutional rights of gays and lesbians – the issue decided Thursday.

“I've been accused of taking this a little too personally, and I accept that critique,” Newsom said.

“I do personally defend Phyllis Lyon and Del Martin when people attack their rights,” he said. “I'm about to get married, and no one's criticized my decision-making, but the fact they can criticize their decision making and they've been together 52 years is remarkable.”

Now a more seasoned politician, last year handily winning a second term as mayor, Newsom is no less outspoken on the issue.

On Thursday, he and City Attorney Dennis Herrera, whose office argued the case before the court, appeared victorious in a news conference, reveling in a deafening chorus of cheers from grateful supporters. Newsom, in a pressed suit and his trademark slick-backed hair, raised his arms and beamed, as the crowd shouted and celebrated the historic moment in the cavernous City Hall rotunda.

“He did stick his neck out on this issue and took a lot of heat, and the court decision vindicated him,” said state Assemblywoman Fiona Ma, D-San Francisco, who sat on the city's Board of Supervisors during the same-sex wedding spree of 2004.

Even Feinstein said the court's decision could indicate a change in public opinion on a divisive issue.

“It's become apparent to me that the views of Californians are changing in this regard, and becoming much more favorable with respect to recognizing the social and economic bonds that marriage provides – regardless of the sex of the individuals,” Feinstein said in a statement.

But all the rejoicing could come to an end if California voters approve a ballot initiative in November that would change the state's constitution to ban same-sex marriage, as has been done in 26 other states. The Secretary of State has not yet determined whether the sponsors have enough signatures to qualify the marriage amendment.

Gov. Arnold Schwarzenegger opposes the idea of an amendment, and Newsom said he will fight it vigorously.

For a politician rumored to have an eye on the 2010 gubernatorial election, it's still uncertain how much political momentum the court victory could give Newsom because the issue is still a divisive one outside of the liberal San Francisco Bay area, Cain said.

“African Americans and Hispanics may be more socially conservative, and in a gubernatorial race, (gay marriage) may not be a winning issue,” Cain said.

“It won't hurt him maybe, but it's not a huge plus. He's got to establish his credentials in something other than social liberalism – like his record on building up the city's economy, reducing crime or some record other than social liberalism.”