The ruling, which comes as the country grapples with a shocking surge in gun crime, overturns a New York law that required person to prove legitimate needs to receive a gun permit.
The US Supreme Court has ruled that Americans have a fundamental right to carry firearms in public, in a landmark decision that came just weeks after another deadly school shooting.
The 6-3 ruling strikes down a New York law that required a person to prove legitimate self-defence needs to receive a gun permit and will prevent states from restricting people carrying guns.
Despite a growing call for limits on firearms after two mass shootings in May stunned the country, the court on Thursday sided with advocates who said the US Constitution guarantees the right to own and carry guns.
Justice Clarence Thomas, who wrote the majority opinion, said the Second and Fourteenth Amendments protect an individual's right to carry a handgun for self-defence outside the home.
President Joe Biden said he was "deeply disappointed" with the ruling. "This ruling contradicts both common sense and the constitution, and should deeply trouble us all," he said in a statement.
The US Senate is currently considering a rare bipartisan bill that includes modest gun control measures.
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'Watershed win' vs 'dark day'
The Supreme Court ruling is the first by the court in a major Second Amendment case in a decade and a victory for the powerful gun lobby, the National Rifle Association.
"Today's ruling is a watershed win for good men and women all across America and is the result of a decades-long fight the NRA has led," NRA executive vice president Wayne LaPierre said in a statement.
"The right to self-defence and to defend your family and loved ones should not end at your home."
The New York law said that to be given a permit to carry a firearm outside the home, a gun owner must clearly demonstrate that it is explicitly needed for self-defence — meaning those without the demonstrated need could not do so.
Gun-rights advocates said that violated the Second Amendment of the Constitution, which says "the right of people to keep and bear arms shall not be infringed."
After Thursday's ruling, New York's governor Kathy Hochul expressed disappointment and called it a "dark day".
"Shocking, absolutely shocking, that they have taken away our rights to have reasonable restrictions," Hochul told reporters, breaking off from a separate announcement.
On May 14, an 18-year-old used an AR-15-type assault rifle to kill 10 African Americans at a supermarket in Buffalo, New York.
Less than two weeks later 19 children and two teachers were shot and killed at an elementary school in Uvalde, Texas, by another teen with the same type of high-powered, semi-automatic rifle.
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