The court refused to hear cases from the states -- Indiana, Oklahoma, Utah, Virginia and Wisconsin -- seeking to keep their same-sex marriage bans in place.
Couples in some of those states began applying for marriage licenses just hours after the Supreme Court's decision.
CNN affiliate WVEC in Norfolk, Virginia, captured a same-sex couple who rushed to fill out their marriage license documents. Officials in Virginia began issuing same-sex marriage licenses at 1 p.m. Monday.
Tony London and Tim Bostic, two plaintiffs in Norfolk, said they were ready to receive their marriage license Monday afternoon.
"It was a pleasure suing you," London joked when a clerk handed him the license, a WVEC reporter tweeted, capturing the two locked in a kiss.
In Richmond, Lindsey Oliver and Nicole Pries left work and drove to the John Marshall Courthouse, where they were the first same-sex couple to be married.
"It's a great thing," Oliver told CNN affiliate WTVR. "There's lot of things that need to be done in Virginia to still make gays equal. This is one step and we're glad to be a part of it."
Colorado Attorney General John Suthers said all of the state's 54 county clerks must start issuing same-sex marriage licenses.
A similar order could be issued by day's end for Indiana and Wisconsin.
"Supreme Court" trended on Twitter with dozens of people weighing in -- and trying to figure out exactly what the high court's move meant.
Experts say its refusal to hear the cases from those five states also means that six more states -- Colorado, North Carolina, South Carolina, Kansas, West Virginia, and Wyoming -- could soon have to lift their bans on same-sex marriage, because they are covered by the same circuit appeals courts that initially struck down the prohibitions.
Once that happens, the number of states permitting same-sex marriage would jump from 19 to 30.
At issue is whether gay and lesbian couples in all 50 states have the same equal protection or due process right to marry that opposite-sex couples have.
The Family Research Council, a conservative public policy and lobbying organization, said voters were having their rights infringed.
"Unfortunately, by failing to take up these marriage cases, the high court will allow rogue lower court judges who have ignored history and true legal precedent to silence the elected representatives of the people and the voice of the people themselves by overturning state provisions on marriage," Family Research Council President Tony Perkins said.
In Utah, just hours after word from the high court came down, Gov. Gary Herbert said at a press conference that he felt "surprised" and "disappointed" that there was no "finality" on the issue of same-sex marriage. The state would comply with Monday's order, he said, and same-sex marriages would move forward.
"Regardless of your personal beliefs," he urged, "... please treat each other with respect and with kindness as we transition through this new law."
The court's action does not mean there won't eventually be a final ruling on the constitutional questions -- many court observers fully expect a landmark decision in the next year or two -- but it does signal the justices are not ready to jump into the politically charged debate right now.
The high court's move surprised many observers. Advocates on both sides of the issue had wanted the court to offer a definitive, binding ruling on key constitutional questions.