The court, in a brief order, said it would hear cases concerning marriage restrictions in Michigan, Kentucky, Ohio and Tennessee. The ruling, due by the end of June, will determine whether 14 remaining state bans will be struck down.
The court said it will decide two questions: Whether states must allows same-sex couples to marry and whether states must recognize same-sex marriages that take place out-of-state. The court will hear an extended two and a half hours of oral arguments in April.
The plaintiffs include two nurses from Michigan, April DeBoer and Jayne Rowse, and Louisville, Kentucky couple Timothy Love and Lawrence Ysunza, who have been in a relationship for 33 years.
"We are excited obviously for our clients and for the many thousands of couples like them in Michigan, but we are also excited for the entire nation," said Dana Nessel, a lawyer for the Michigan plaintiffs.
"We are now that much closer to being fully recognized as a family, and we are thrilled," DeBoer said in a statement.
Most of the states that are defending state bans had, like the gay rights advocates, urged the high court to take up the issue in order to resolve the legal uncertainty.
Supporters of gay rights have touted same-sex marriage as one of the leading American civil rights issues of this era. Gay right groups quickly urged the justices to issue a nationwide ruling endorsing the legality of gay marriage.
"It’s time for America to no longer be a house divided when it comes to the freedom to marry," said Brian Silva, executive director of the group Marriage Equality USA.
Chad Griffin, president the Human Rights Campaign, called the pending high court ruling the "moment of truth."
There has already been a legal sea change on the issue, thanks in large part to the Supreme Court’s prompting. It began in earnest in June 2013 when the court struck down a federal law that restricted, for the purpose of federal benefits, the definition of marriage to heterosexual couples.
Judges around the country later seized on the language in the decision, written by swing vote Justice Anthony Kennedy, to strike down a series of state bans.
At the time of the 2013 ruling, only 12 states had authorized gay marriage. It is now legal in 36 of the 50 states.
Michigan Attorney General Bill Schuette, a Republican who is defending the state's ban, welcomed the court's announcement, saying the state and nation "will be well served" by a definitive ruling on the issue.
Although the gathering momentum toward gay marriage has been prompted largely by the courts, opinion polls show that support among Americans has been rising in recent years. But many conservative Christians remain steadfastly opposed.
"We are hopeful the Supreme Court will uphold the freedom of the people to affirm marriage," said Austin Nimocks, a lawyer with conservative Christian legal group Alliance Defending Freedom.
The court’s expected ruling in June would come as the field of candidates for the 2016 U.S. presidential election takes shape, and the issue could factor into the race. Democrats are generally in favor of gay marriage while Republicans are divided on the issue.
The primary legal issue is whether the state bans and the refusal to recognize out-of-state marriages violates the U.S. Constitution's guarantee of equal protection under the law.
As recently as October, the court decided not to intervene in the gay marriage issue when seven cases from five states were pending. That decision not to hear the disputes had huge legal implications because it meant that gay marriage went ahead in five states and paved the way for it to begin in several others.
A Nov. 6 decision by the Cincinnati-based 6th U.S. Circuit Court of Appeals to uphold marriage restrictions in four states increased pressure on the Supreme Court to take up the matter. It was the first of the nation's regional federal appeals courts to uphold gay marriage prohibitions after the wave of other rulings declaring the bans unconstitutional.
The Supreme Court is divided on gay rights, with Kennedy likely to be the key vote. It is not known how he would rule on gay marriage but he has a history of backing gay rights.
Litigation in other cases continues in lower courts. Last week, a federal appeals court in New Orleans heard oral arguments over gay marriage bans in Texas, Louisiana and Mississippi. Earlier this week, a judge in South Dakota struck down that state's ban.