Despite the potentially wide-ranging implications of the administration's brief, it still falls short of what gay rights advocates and the attorneys who will argue against Proposition 8 had hoped for. Those parties had pressed the president to urge the Supreme Court to not only overturn California's ban, but also declare all gay marriage bans unconstitutional.
Still, marriage equality advocates publicly welcomed the president's legal positioning.
"Obama again asserted a bold claim of full equality for gay Americans, this time in a legal brief," said Richard Socarides, an attorney and advocate. "If its full weight and reasoning are accepted by the Supreme Court, all anti-gay marriage state constitutional amendments will fall, and quickly."
The National Organization for Marriage, a leading supporter of the California ban, rejected Obama's arguments. Spokesman Thomas Peters said he expects the Supreme Court to uphold the votes of more than 7 million Californians to protect marriage, spokesman Thomas Peters said.
The president raised expectations that he would back a broad brief during his inaugural address on Jan. 21. He said the nation's journey "is not complete until our gay brothers and sisters are treated like anyone else under the law."
"For if we are truly created equal, than surely the love we commit to one another must be equal as well," he added.
Obama has a complicated history on gay marriage. As a presidential candidate in 2008, he opposed the California ban but didn't endorse gay marriage. He later said his personal views on gay marriage were "evolving."
When he ran for re-election last year, Obama announced his personal support for same-sex marriage but said marriage was an issue that states, not the federal government, should decide.
Public opinion has shifted in support of gay marriage in recent years.