For 15 years, a law in the United States defined marriage to be between a man and a woman. But in a policy shift, the government has announced that it will no longer support the legislation.
The decision was made after a detailed review in recent weeks, Attorney General Eric Holder said on Wednesday.
In 1996, President Bill Clinton signed into law the Defense of Marriage Act that barred the federal recognition of same-sex marriages and denied same-sex couples federal benefits that are available to married couples.
The government said it now agrees with a ruling by a Boston judge in 2010 that banning gay marriages was unconstitutional.
Same-sex marriages are legalised in five states out of 50. Some other states have adopted civil unions, a concept that President Barack Obama has supported in the past. Obama said in December that on the subject of gay and lesbian marriages “I struggle with this,” and that his views were “constantly evolving.”
For gay rights activists this is a second chance to celebrate in about two months. In December, the government lobbied the Congress to lift a ban against gay people serving openly in the military.
Conservatives have criticised the move as political. Mike Huckabee, a presidential candidate in 2008, told reporters that Obama’s decision “was an absolutely boneheaded political move,” according to Reuters.
euronews’ London correspondent