Gay marriage is legal in Vermont after the House voted 100-49 to override a veto from state Governor Jim Douglas.
Earlier today, the Senate voted 23-5.
The House needed a two-thirds majority to override the veto.
Vermont is the fourth US state after Massachusetts, Connecticut and Iowa to allow gay marriage. It is the first state to do this with a legislature’s vote.
Civil unions in Vermont were legalised in 2000 but offered only some of the benefits available to straight married couples.
Although the new bill will not guarantee federal benefits to same-sex couples, they will be granted access to Social Security benefits available to straight married couples.
They would also be able to claim joint health insurance and make emergency medical decisions.
Opponents argued the bill would undermine traditional marriage, render men and women interchangeable and destroy the connection between children and marriage.
However, polls showed citizens were in favour of the move.
A poll of 7,000 Vermont citizens last March showed that 54 per cent supported gay marriage, while only 37 per cent were opposed. A smaller survey taken in January suggested that 58 per cent were in favour of or leaning towards gay marriage.
Some critics have questioned why the cash-strapped state should be focusing on gay marriage at this time, but figures from the Williams Institute have suggested that extending marriage rights to gay couples will boost Vermont’s economy by over $30.6 million in three years.
Last week, Iowa voted to legalise gay marriage.