He was 79. He died of apparent natural causes, in his sleep after a day of quail hunting outside El Paso, Texas. He was staying at a private residence in the Big Bend area of South Texas. He was found dead Saturday morning when he did not appear for breakfast, a Marshals Service spokeswoman said.
Scalia, the longest-serving justice on the Supreme Court, taught at the University of Chicago from 1977 to 1982.
He was nominated to the U.S. Supreme Court in 1986 by President Ronald Reagan.
GOP Senate Leader Mitch McConnell and other Republicans said the Supreme Court vacancy should not be filled until there is a new president in January 2017.
However, President Barack Obama said he plans to fulfill his constitutional responsibility and nominate a successor to fill the vacancy. In a direct rebuttal to Senate Republicans, Obama said there is plenty of time for the Senate to confirm his choice.
Obama pointedly calls the decision "bigger than any one party." He says it is about democracy.
Obama also praised the late justice as a brilliant legal mind who influenced generation of lawyers and students.
Scalia is survived by a wife and nine children.
Texas Gov. Greg Abbott said in a statement: "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. His fierce loyalty to the Constitution set an unmatched example, not just for judges and lawyers, but for all Americans. 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."
READ: Reactions from other public figures
While our opinions were frequently at odds Justice Scalia remained true to his beliefs in 3 decades of service. My thoughts are w his family— Senator Dick Durbin (@SenatorDurbin) February 13, 2016
Chief Justice John G. Roberts, Jr. said in a statement: "On behalf of the Court and retired Justices, I am saddened to report that our colleague Justice Antonin Scalia has passed away. 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 so loyally served. We extend our deepest condolences to his wife Maureen and his family."
Scalia used his keen intellect and missionary zeal in an unyielding attempt to move the court farther to the right and to get it to embrace his "originalist" view of judging after his 1986 appointment by President Ronald Reagan.
His 2008 opinion for the court in favor of gun rights was his crowning moment in more than 30 years on the bench.
He was a strong advocate for privacy in favoring restrictions on police searches and protections for defendants' rights. But he also voted consistently to let states outlaw abortions, to allow a closer relationship between government and religion, to permit executions and to limit lawsuits.
Scalia's impact on the court was muted by his seeming disregard for moderating his views to help build consensus.
The Associated Press contributed to this report.