Heyerdahl stopped taking food, water or medication in early April after being diagnosed with a terminal brain tumor. Relatives said he died in his sleep at a hospital near his family retreat at Colla Michari, Italy.
Experts scoffed at Heyerdahl when he set off to cross the Pacific aboard a balsa raft in 1947, saying it would get water logged and sink within days.
After 101 days and 4,900 miles, he proved them wrong by reaching Polynesia from Peru, in a bid to prove his theories of human migration.
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In 1978, he sailed in the Middle East and Indian Ocean on the Tigris reed vessel, to mimic ancient trade routes.
His wide-ranging archaeological studies were often controversial and challenged accepted views. He insisted that the world had got marine design wrong. He said he felt far safer in a storm on a small, buoyant craft that simply popped up after a battering from waves than on a giant modern ship with a rigid hull.
He built his theories on simple observations - pyramids built by the Aztecs in Mexico are similar to those in Egypt, while dogs and sweet potatoes on Pacific islands are like those in South America.
"Many scientists have always viewed me like a daredevil who's gone over Niagara Falls in a barrel," he once grumbled. "I was bitter many times. When you are accused of humbug, then you are bitter. But not now."
Heyerdahl maintained a high pace of research, lectures and travel until his sudden illness.
Last year, he issued a book, "The Hunt for Odin," saying that the Nordic god might have been inspired by a king who lived in what is now southern Russia 2,000 years ago.
Earlier this year, he traveled to Samoa in the Pacific, where he took part in archaeological studies of a discovery that could be an ancient pyramid.
"He died ... with his family by his side, quietly and peacefully," his eldest son, Thor Heyerdahl, Jr., told Reuters. "He did not wake during the past three days."
He spent his final days surrounded by family at Colla Michari, a Roman-era Italian village he bought and restored in the 1950s. His permanent home since 1990 was on the Spanish island Tenerife in the Atlantic Ocean off the coast of Morocco.
Though he lived and worked abroad for decades, Heyerdahl was a national hero in his homeland, a maritime nation of 4.5 million people that voted him Norwegian of the Century in a 1999 newspaper poll. Heyerdahl was a frequent visitor to Norway, where the Kon-Tiki museum in Oslo maintained an apartment for his use.
Heyerdahl was born Oct. 6, 1914, in the southern Norwegian town of Larvik. He was the son of a widely traveled banker and a mother with a scientific bent. He said she gave him anthropology books instead of children's books to read when he was sick in bed.
He had nearly drowned twice as a child in Larvik and overcame his fear of water only at age 22, when he fell into a raging river in Tahiti and swam to safety.
"If you had asked me as a 17-year-old whether I would go to sea on a raft, I would have absolutely denied the possibility. At that time, I suffered from fear of the water," Heyerdahl once said.
Heyerdahl is succeeded by his third wife Jaqueline, four of his five children, eight grandchildren and six great-grandchildren.
Funeral plans were not immediately announced.