He passed Tuesday after a brief illness at Johns Hopkins Hospital, The Baltimore Sun reported Wednesday.
Announcing the author's death, his publisher, Ivan Held, president of G.P. Putnam's Sons, did not give a cause of death, The New York Times reported.
Four of his novels have been turned in feature films. His novel "The Hunt for Red October" had made $1.3 million four years after it was published in 1984.
Born April 12, 1947, in Baltimore, Clancy ran an insurance agency before branching out into writing.
He became part owner of the Baltimore Orioles in 1993 and agreed to purchase the Minnesota Vikings in 1998. However, the cost of his divorce from his first wife, Wanda, forced him to abandon that plan.
Clancy married Alexandra Marie Llewellyn, a freelance journalist, in 1999.
His next book, "Command Authority," is scheduled to be published Dec. 3.