The House voted 100-49, just reaching the required two-thirds vote to negate a governor's veto under Vermont law. The Senate earlier squashed the veto on a vote of 23-5.
Same-sex couples can begin receiving civil marriage licenses on Sept. 1, when the law is set to take effect.
The House chamber erupted with cheers and applause as House Speaker Shap Smith, D-Morristown, announced the results, his voice cracking. "You have overridden the veto," Smith said, before quickly calling the House to order, ending the celebration.
Douglas, who called the issue of same-sex marriage a distraction, said it was now time for lawmakers to turn their attention to the state's budget and economic woes. "What really disappoints me is that we have spent some time on an issue, during which another thousand Vermonters have lost their jobs. We need to turn our attention to balancing a budget without raising taxes, growing the economy, putting more people to work," Douglas told The Associated Press. The fate of the bill was uncertain heading into the override vote.
The House secured only 95 votes last week when it passed the measure. Lawmakers and members of the public sat quietly in suspense Tuesday through the roll call vote, many keeping a running tally.
The Legislature's override of the veto brings to an end several weeks of debate on the emotional, and at times divisive, debate. Lawmakers heard testimony from people with varying backgrounds, and were bombarded with calls, e-mails and letters from constituents urging them to vote one way or the other.
Douglas' announcement that he intended to veto the bill set off a furious push by supporters of the legislation to garner enough votes for an override.
In recent days, the Democratic caucus put immense pressure on the 11 Democrats who voted against the bill last week, including two local representatives, to vote with the Democratic party on the override, several lawmakers said.
Reps. Cynthia Browning, D-Arlington, and Timothy Corcoran II, D-Bennington, didn't budge, however, and both voted to sustain Douglas' veto.
"I'm probably now in the doghouse. I'm going to be in the outhouse, and probably soon in the wilderness," Browning said. "I'm very proud of my vote, and I'm very proud that I stood up for what I believe in." Her position, she argued, is the same position President Barack Obama expressed during his presidential campaign.
Browning said fellow Democrats suggested she would lose her seat if she voted against the party, and that she should perhaps "get sick and miss the vote," she said. But she was never offered anything for her vote. "I think they know me better than that," Browning said.
The vote result was not unexpected, Browning said, because party leaders who initially approached her about changing her position gave up. "Last week, I was under so much pressure that I told the Speaker I would talk to him and only him, that others should leave me alone.
He didn't come back to me, so I figured he got someone else to flip," she said.
Vermont became the first state in the nation to approve civil unions nine years ago.
It is now the fourth state to allow same-sex marriage, following Massachusetts, Connecticut and Iowa.
But Vermont is the first of the four states allowing gay couples to wed to do so through legislation. The first three states were the result of court orders.
Douglas, a Republican in his fourth term, vetoed the same-sex marriage bill Monday evening after promising to do so on March 26. In his veto message, he said he was returning the bill to the Legislature because it would do nothing to ensure federal benefits for same-sex couples, and because he believes marriage should remain between a man and a woman.
Supporters of the bill were exultant, including Senate President Pro Tem Peter Shumlin, who along with Smith, said just a few weeks ago that passing a same-sex marriage bill would be a priority for the Legislature.
"Today Vermont legislators did the right thing by overriding Gov. Douglas' veto and granting equal rights to all Vermonters," he said. "Today is another historic day for Vermont, and I have never felt more proud as we become the first state in the country to enact marriage equality not as the result of a court order, but because it is the right thing to do."
Opponents, such as Steven Cable of Vermont Renewal, said they were saddened by the outcome.
"Today is a very sad day in Vermont political history, and Vermont's long-standing reliance on common sense and the natural order," he said. "The most fundamental institution of any society, marriage, has been redefined in just three short weeks with the influence of hundreds of thousands of dollars from out-of-state, and a process that limited and stacked debate using political muscle."
Before the Senate voted, Shumlin urged his colleagues to support the override to end the debate on the issue, saying proponents would continue to introduce the legislation until it was approved.
"This discussion will continue until marriage equality is available to all Vermonters," he said.
Contact Neal P. Goswami at email@example.com