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The ruling will not apply pending a possible appeal. Same-sex marriages are legal in 17 US states, most of them in the north-east, and Washington DC.
Such unions have been approved either through legislation, court rulings or voter referendums.
'Adding momentum' The ruling by Judge Arenda Wright Allen in Norfolk followed a legal challenge on same-sex marriage by a gay couple.
The judge agreed with them that the ban infringes on their constitutional rights and their fundamental freedom to marry.
Many expect the case - or one like it - to go all the way to the US Supreme Court, the BBC's Beth McLeod in Washington reports.
Virginia is the first state in the old confederacy - a group of southern states that are traditionally seen as socially conservative - to have its ban overturned.
The decision adds momentum to a growing acceptance of gay marriage in the US, our correspondent adds.
Earlier this week, a federal judge in Kentucky - another southern state - ruled that it must recognise same-sex marriages performed elsewhere in the US.
However, the judge did not rule on the legality of same-sex marriages inside Kentucky, effectively meaning that the current ban remained in place.
A US federal judge in Virginia has ruled that the state's ban on same-sex marriage is unconstitutional.
It is the first time that a southern state has had a voter-approved prohibition on gay marriage overturned.The ruling will not apply pending a possible appeal. Same-sex marriages are legal in 17 US states, most of them in the north-east, and Washington DC.
Such unions have been approved either through legislation, court rulings or voter referendums.
'Adding momentum' The ruling by Judge Arenda Wright Allen in Norfolk followed a legal challenge on same-sex marriage by a gay couple.
The judge agreed with them that the ban infringes on their constitutional rights and their fundamental freedom to marry.
Many expect the case - or one like it - to go all the way to the US Supreme Court, the BBC's Beth McLeod in Washington reports.
Virginia is the first state in the old confederacy - a group of southern states that are traditionally seen as socially conservative - to have its ban overturned.
The decision adds momentum to a growing acceptance of gay marriage in the US, our correspondent adds.
Earlier this week, a federal judge in Kentucky - another southern state - ruled that it must recognise same-sex marriages performed elsewhere in the US.
However, the judge did not rule on the legality of same-sex marriages inside Kentucky, effectively meaning that the current ban remained in place.