In a splintered 6-3 ruling, the court upheld Indiana's strict photo ID requirement, which Democrats and civil rights groups said would deter poor, older and minority voters from casting ballots. Its backers said it was needed to deter fraud.
It was the most important voting rights case since the Bush v. Gore dispute that sealed the 2000 election for George W. Bush.
The law "is amply justified by the valid interest in protecting 'the integrity and reliability of the electoral process,"' Justice John Paul Stevens said in an opinion that was joined by Chief Justice John Roberts and Anthony Kennedy.
"This is a big win for Republicans, who have fought all across the country for more stringent voting requirements. And it's a big loss for Democrats, who argued to the Justices that the restrictive law would preclude many of their voters from being able to exercise their right to choose a candidate," says CBS News chief legal analyst Andrew Cohen.
Justices Samuel Alito, Antonin Scalia and Clarence Thomas also agreed with the outcome, but wrote separately.
Justices Stephen Breyer, Ruth Bader Ginsburg and David Souter dissented.
More than 20 states require some form of identification at the polls. Courts have upheld voter ID laws in Arizona, Georgia and Michigan, but struck down Missouri's. Monday's decision comes a week before Indiana's presidential primary.
"We'll see lots of action now on this front in advance of the general election in November," Cohen says.
The case concerned a state law, passed in 2005, that was backed by Republicans as a way to deter voter fraud. Democrats and civil rights groups opposed the law as unconstitutional and called it a thinly veiled effort to discourage elderly, poor and minority voters - those most likely to lack proper ID and who tend to vote for Democrats.
There is little history in Indiana of either in-person voter fraud - of the sort the law was designed to thwart - or voters being inconvenienced by the law's requirements.
"We cannot conclude that the statute imposes 'excessively burdensome requirements' on any class of voters," Stevens said.
Stevens' opinion suggests that the outcome could be different in a state where voters could provide evidence that their rights had been impaired.
But in dissent, Souter said Indiana's voter ID law "threatens to impose nontrivial burdens on the voting rights of tens of thousands of the state's citizens."
Scalia, favoring a broader ruling in defense of voter ID laws, said, "The universally applicable requirements of Indiana's voter-identification law are eminently reasonable. The burden of acquiring, possessing and showing a free photo identification is simply not severe, because it does not 'even represent a significant increase over the usual burdens of voting."'