This is a breaking news item.
"Justice Antonin Scalia was a man of God, a patriot, and an unwavering defender of the written Constitution and the Rule of Law. He was the solid rock who turned away so many attempts to depart from and distort the Constitution," Texas Gov. Greg Abbott said in a statement.
"We mourn his passing, and we pray that his successor on the Supreme Court will take his place as a champion for the written Constitution and the Rule of Law," the governor added.
The circumstances surrounding his death were not immediately confirmed by NBC News.
Chief Justice Roberts said that he and his fellow justices were saddened to learn of his death.
"He was an extraordinary individual and jurist, admired and treasured by his colleagues. His passing is a great loss to the Court and the country he loyally served," Roberts said in a statement.
More from NBC News:
The court's most influential conservative, Scalia was nominated in 1986 under President Ronald Reagan, who named him as associate justice. A lawyer by trade, Scalia entered public service in the 1970s as general counsel for President Richard Nixon and as the assistant attorney general.
At the time of his Supreme Court nomination, Scalia was confirmed unanimously — 98 to zero — after telling senators he had no plans to reshape the law.
"I am not going onto the court with a list of things I want to do. My only agenda is to be a good judge," he said.
But he quickly became one of the court's most outspoken conservatives, serving as a steadfast opponent of gay rights and affirmative action in hiring and school admissions, and abortion rights. The landmark case of Roe v. Wade, he said, was wrongly decided, declaring rights that the founding fathers never intended.
"Abortion, homosexual conduct ... Nobody ever thought that they had been included in the rights contained in the Bill of Rights," he said once.
The nation's first Italian-American justice, Scalia didn't sugarcoat his often blunt dissents.
Most recently, in December, he came under fire from civil rights attorneys and black lawmakers after suggesting African-American students might fare better in a "slower-track school" while hearing a case about race-based admissions.
But it was his comments over the years on gay rights that often caused the biggest waves: When the high court legalized gay marriage nationwide last June, Scalia said in his dissent: "Who ever thought that intimacy and spirituality [whatever that means] were freedoms?"
"And if intimacy is, one would think that Freedom of Intimacy is abridged rather than expanded by marriage. Ask the nearest hippie," he wrote.
His candor wasn't limited to the four walls of the high court. During a 2012 visit to Princeton University, a gay freshman asked Scalia about a comparison he had drawn in the past between banning sodomy and banning bestiality and murder.
"If we cannot have moral feelings against or objections to homosexuality, can we have it against anything?" Scalia said in response to the question, according to The Daily Princetonian.
Though generally unsympathetic to criminal suspects, he led the court in expanding the rights of defendants to confront their accusers in court and limiting a judge's power to use evidence in sentencing unless it was proved during a trial.
And he wrote the ruling that said the Second Amendment guarantees an individual's right to own a firearm, the court's most important gun case ever.
The last Supreme Court justice to die while serving was Chief Justice William Rehnquist, 80, in September 2005. Rehnquist was the first to die in office since Justice Robert Jackson in 1954 and the first Chief Justice since Fred Vinson in 1953.
Obama had been notified of Scalia's death, the White House said. Obama expressed sympathy and would have a statement later, the White House added.
Former President George W. Bush called Scalia a "towering figure and important judge."
"He brought intellect, good judgment, and wit to the bench, and he will be missed by his colleagues and our country," he said.
Scalia was slated to teach in Paris this summer for the San Diego-based Thomas Jefferson School of Law. He and his wife, Maureen, have nine children.