Denton died at a hospice facility in Virginia Beach, Virginia, from a heart ailment, his family said.
The retired Navy rear admiral was elected in 1980 as Alabama's first Republican senator in 112 years and earned a reputation as one of the Senate's most conservative members before being defeated in his 1986 re-election bid. President Ronald Reagan lauded him that year as a national treasure.
President Barack Obama said in a statement that Denton "leaves behind a legacy of heroic service to his country."
He said: "The valour that he and his fellow PoWs displayed was deeply inspiring to our nation at the time, and it continues to inspire our brave men and women who serve today.".
Denton was most famous for spending seven years and seven months as a Vietnam War PoW after his plane was shot down during a bombing mission from the aircraft carrier USS Independence in 1965.
Imprisoned in brutal conditions in and around Hanoi, Denton encouraged fellow American prisoners to resist their North Vietnamese captors.
American PoWs were sometimes paraded in propaganda films and in 1966, the captive Denton was interviewed for such a film - it later aired on US television - apparently in the hope that he would denounce the US war policy.
"Well, I don't know what is happening," he told his interviewer. "But, whatever the position of my government is, I support it fully. And whatever the position of my government is, I believe in it - yes, sir. I'm a member of that government and it is my job to support it. And I will as long as I live."
During the interview, he pretended to have light sensitivity that caused him to blink his eyes. What he was actually doing was blinking in Morse Code to spell out "t-o-r-t-u-r-e".