Chicago resident Otis McDonald challenged that city's handgun ban, saying he needed to protect himself.
"If I see innocent and law-abiding citizens on the streets with guns, I'll be safe," said McDonald. "I'll feel safe because they're not going out there breaking the law."
Today the Court said, ruling individuals have a fundamental right to protect themselves, reports CBS News chief legal correspondent Jan Crawford.
The case split the Court sharply along conservative and liberal lines.
Writing for the majority, Justice Samuel Alito reaffirmed a decision two years ago that the Constitution's Second Amendment protects an individual's right to "keep and bear arms" for self defense. That decision struck down Washington D.C.'s handgun ban.
But today's decision resolved a huge question: Did that landmark decision to other cities and states, or only to Washington DC?
The Court settled it today: The Second Amendment, Alito wrote, "applies equally to the federal government and the states."
Retiring Justice John Paul Stevens, in his last day on the Court, said in dissent, that the ruling would prove "destructive…to our nation's communities and to our constitutional structure."
The ruling was a victory for the NRA, which has fought for decades to establish a constitutional right to own guns.
"It's a vindication for the great majority of Americans all across this land," said NRA CEO Wayne LaPierre.
But the Court emphasized the right was not absolute. Cities and states can pass reasonable restrictions on gun ownership.
"We feel confident that communities and states will be able to decide things now to keep their communities safe," said Paul Helmke, President of the Brady Center to Prevent Gun Violence.
But even though today's ruling says cities and states can't ban handguns outright, today's ruling is certain to lead to more lawsuits over exactly what kind of restrictions they can impose.