(RNN) –The U.S. Supreme Court in a 5-4 vote has struck down the Defense of Marriage Act.
"DOMA singles out a class of persons deemed by a State entitled to recognition and protection to enhance their own liberty," the decision reads.
The opinion is applies to those already married.
Dissenting justices are Chief Justice John Roberts, Antontin Scalia, Clarence Thomas and Samuel Alito.
A decision on California's Proposition 8 is forthcoming.
Hundreds of people on both sides of the gay marriage debated began assembling outside the Supreme Court Building in the morning to voice their opposition or support for the current laws.
Hearings on the arguments for the two cases originally took place March 26 and 27.
There are 12 states where gay marriage is or will soon become legal: New York, New Hampshire, Massachusetts, Vermont, Maine, Rhode Island, Connecticut, Maryland, Delaware, Iowa, Washington and Minnesota, as well as Washington, DC.
All of these states vary in how spousal support or broad domestic partnership rules apply despite their state's legislation, i.e., equal protection laws.
The case of United States v. Windsor argues for equal protection of rights for couples legally married in states that recognize same-sex marriages. The case seeks to protect those couples if after marriage they reside in a state that "deprives same-sex couples who are lawfully married under the laws of their states (such as New York) of the equal protection of law, as guaranteed by the Fifth Amendment."
Signed in 1996 by President Bill Clinton, DOMA says "the word 'marriage' means only a legal union between one man and one woman as husband and wife," and the term "'spouse' refers only to a person of the opposite sex." President Clinton now speaks in favor of same sex marriages, and champions DOMA's repeal.
"As the president who signed the act into law, I have come to believe that DOMA is contrary to those principles and, in fact, incompatible with our Constitution," Clinton said earlier this year.
The state of California - along with Colorado, Illinois, Hawaii and New Jersey - allows legal civil unions. These states are some of the earliest in the U.S. to have such arrangements for same-sex couples.
California's Proposition 8, voted into law in November 2008, enforces the same principle on the state level - banning marriage for same-sex couples. The decision was made in the voting booth, and since its inception it has been challenged.
The rest of the United States' laws on gay marriage vary from either a county-to-county basis to statewide bans, with many states having longstanding bans and referendums on the books since the early to mid-1990s.