The ex-guerrilla who governed Uruguay from 2010 to 2015 was known as the world's "poorest president" because of his modest lifestyle.
Current President Yamandú Orsi announced his predecessor's death on X, writing: "thank you for everything you gave us and for your deep love for your people."
The politician's cause of death is not known but he had been suffering from oesophageal cancer.
His global popularity is unusual for a president of Uruguay, a country with just 3.4 million inhabitants where his legacy has also generated some controversy.
In fact, even though many tended to see Mujica as someone outside the political class, that was not the case.
He said his passion for politics, as well as for books and working the land, was passed on to him by his mother, who raised him in a middle-class home in Montevideo, the capital city.
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