Buckley suffered from diabetes and emphysema, his son Christopher said, The cause of death was not known immediately, The New York Times reported.
"I'm devastated to report that our dear friend, mentor, leader, and founder William F. Buckley Jr., died overnight in his study in Stamford, Connecticut," National Review Editor Kathryn Jean Lopez posted on the magazine's Web site. "After year of illness, he died while at work; if he had been given a choice on how to depart this world, I suspect that would have been exactly it. At home, still devoted to the war of ideas."
Buckley hosted one of television's longest-running programs, "Firing Line," wrote a syndicated column, penned numerous books and was popular on the lecture circuit.
He vaulted to national prominence with his 1950 book "God and Man at Yale," in which he scolded Yale professors for promoting liberalism and atheism.
Buckley is preceded in death by his wife, Patricia. Besides his son Christopher, Buckley is survived by three sisters, two brothers, a granddaughter and a grandson.