The law bans certain semi-automatic assault weapons and large capacity magazines.
Although the decision comes days after the Orlando shooting, that event probably didn't move the justices either way. In recent years the Court has declined to take up a major Second Amendment case. In 2008, 5-4 Supreme Court held in District of Columbia v Heller that the Second Amendment protects an individual's right to bear arms, and except for a follow up decision two years later, the court has not weighed in again.
Since then, a raging debate has developed between gun rights supporters who say that lower courts are not heeding supreme court precedent and gun control activists who say they are pushing for what they consider reasonable restrictions.
"The Supreme Court's decision to let stand Connecticut's assault weapons restrictions, is just the latest indication that Courts almost universally recognize that common sense life-saving gun laws are fully compatible with the Second Amendment, " said Jonathan Lowy, director of the Legal Action Project at the Brady Center to Prevent Gun violence.
"The fact that Connecticut chose to restrict assault weapons like the ones used in the Orlando and Sandy Hook mass shootings was both reasonable and constitutional," he said.
Gun rights groups -- the plaintiffs in Shew v. Malloy -- had hoped the Supreme Court would step in to clarify the Heller decision.
Scott Wilson Sr., president of the Connecticut Citizens' Defense League, a gun rights group, issued a statement saying that his group fully intends "to renew our challenge to Connecticut's blatantly unconstitutional ban as soon as there are five Justices sitting on the Supreme Court committed to the proper understanding of the Second Amendment."
To do so, Wilson would need to find another challenger to bring up the case. It is a long-shot strategy, especially if the seat of the late Justice Antonin Scalia is filled by a nominee from a Democratic president.
The Heller decision was written by the late Scalia and is considered one of the most important cases of his legacy.
Connecticut's law was passed after the shooting at Sandy Hook Elementary School in Newtown, Connecticut, in December 2012, when 20 students and six educators were killed, and expanded the list of assault weapons that had already been prohibited in the state.
In court papers, state Attorney General George Jepsen said the law was aimed at restricting access "to firearms that are owned by a small percentage of gun owners and are disproportionately used in gun crime, particularly the most heinous forms of gun violence." He added, "The shooter fired 154 rounds with devastating accuracy and efficiency with a firearm that was designed for killing human beings in close quarters, an AR-15 type rifle."