Some legal experts had predict the court would decline to take the Prop 8 appeal at all.
The Obama Administration has officially entered the legal same-sex marriage battle.
NBC's Pete Williams first reported that the Justice Department would urge the United States Supreme Court to allow same-sex marriage to resume in California in an official filing to the court.
The Obama Administration filed a friend-of-the-court brief by the close of business Thursday. Read brief here (pdf).
In it the administration argues that denying gays and lesbians the right to marry violates the Constitution's Equal Protection Clause. It also contends that discrimination based on sexual orientation requires extra scrutiny by the court.
The official filing is specifically in support of the two gay couples who launched the legal fight over Proposition 8 four years ago. Prop 8 is a ballot initiative approved by 52-percent of California voters in 2008. It banned gay marriage and put an end to same sex unions in California. Prior to the vote some 18,000 gay couples were legally married in California.
California is one of eight states that give gay couples all the benefits of marriage through civil unions or domestic partnership, but don't allow them to wed.
California's Lt. Governor Gavin Newsom, who while serving as mayor of San Francisco was the first elected official to allow same sex marriages to happen in 2004, applauded the White House for standing up for equal protection under the law.
"I'm proud of him he's taking a risk he didn't need to do this but he's doing the right thing," Newsom said.
The administration brief argues that grant the benefits shows the state already acknowledges that gay relationships are equal to heterosexual ones.
"They establish homes and lives together, support each other financially, share the joys and burdens of raising children, and provide care through illness and comfort at the moment of death,'' the administration said in the brief.
Gay rights supporters had been pressing the administration to file the brief.
The president was not required to file a brief, though he raised expectations in his second inaugural address when he declared that gays and lesbians must be "treated like anyone else under the law."
The filing is not legally binding. Thursday was the last day for filing briefs in support of the California couples' position.
If the justices agree with administration's filing it could result in gay marriage becoming legal in the seven other states,according to experts. The states are Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon and Rhode Island.
Supreme Court justices have scheduled to hear arguments in the Prop. 8 case at the end of March.
The news of the Justice Department filing came on the same day as a new poll that showed a majority of Californians now support gay marriage.
The Field Poll found a record 61 percent of Californians now approve of allowing same-sex couples to marry. The poll results represent a reversal in views about the issue in the 36 years the Field Poll has been taking surveys on gay marriage. In 1977, when the first survey was conducted, only 28 percent approved of gay marriage, while 59 percent were opposed.