The cases will probably be heard in historic sessions at the court in late March, with decisions to come when the justices finish their work at the end of June.
The court’s first review of same-sex marriage comes at a fast-moving but unsettled time in the nation’s consideration of gay rights. Last month brought Election Day victories for same-sex marriage supporters in three states, including Maryland, and the reelection of President Obama, the first chief executive to endorse the right of gays to marry.
But the vast majority of states ban such unions, and 31 of them have amended their constitutions to enshrine the traditional definition of heterosexual marriage.
The acceptance of the same-sex marriage cases heralds a landmark term for the court on civil rights issues; it had already agreed to consider whether racial preferences may play a role in college admissions and the future of a key part of the Voting Rights Act of 1965 enacted to protect minorities.
The court was almost obliged to review the 1996 Defense of Marriage Act (DOMA), which defines marriage as between a man and a woman and withholds federal benefits from same-sex couples legally married in the states where they live. The law affects things such as health insurance, taxes and medical leave.
Obama announced in 2011 that his administration would no longer defend the law against challenges that it violated the Constitution’s guarantee of equal protection. Four district courts and two courts of appeal have declared the law unconstitutional, including in the New York case, and the high court almost always weighs in on such decisions.
But the court took a bold step in agreeing to review a lower court’s ruling overturning Proposition 8, the 2008 measure in which Californians amended their state constitution to ban same-sex marriage. The referendum came after the state Supreme Court had ruled that there was a right to same-sex marriage and 18,000 couples had taken advantage of the move.
The decision to take the California case raised the possibility that the court would grapple directly with fundamental questions about the right to marry.
The acceptance of the two cases give the justices the ability to take a broad look at gay rights and marked a dramatic moment in the nation’s history.
“This is a momentous case,” said Washington lawyer Theodore Olson, a Republican former solicitor general who combined with Democratic attorney David Boies to bring the challenge to Proposition 8. “It will be an education for the American people, and we are very confident that the outcome of this case will be to support the marriage rights of our gay and lesbian brothers and sisters.’’