Guterres, widely known by his nom de guerre "Lu Olo", died on Sunday at Prince Court Medical Centre in Kuala Lumpur, Malaysia, where he had been in intensive care, his family said on the late president's official Facebook account.
The cause of death was not immediately disclosed.
Guterres served as president from 2017 to 2022, capping decades of involvement in the political and armed struggle that led to independence for Southeast Asia's youngest nation in 2002.
"Throughout his life, he remained committed to the freedom of his people and the building of a democratic nation," Malaysian Prime Minister Anwar Ibrahim said in a message of condolences to his family and the people of East Timor, also known as Timor-Leste.
Fretilin, the party Guterres had led for years, said his death was a "profound loss" for all those who shared the goal of building a free, democratic and sovereign country.
The party highlighted his lifelong dedication to the independence movement and his role in promoting national unity, dialogue, peace and political stability throughout his public career.
Born on September 7, 1954, in Ossu, a town of Viqueque District, in what was then Portuguese Timor, he rose to prominence in the resistance against Indonesia's occupation from 1975 to 1999.
As a senior leader of Fretilin, he later played a key role in the transition to independence following a United Nations-backed referendum in 1999.
He served as president of the Constituent Assembly in 2001, overseeing the drafting of East Timor's constitution, and became the first speaker of the National Parliament after independence in 2002.
After several unsuccessful bids, he was elected president in 2017 and served one term.
He lost a re-election bid in 2022 to current President Jose Ramos-Horta, his fellow independence fighter.
Guterres is survived by his wife, Cidalia Lopes Nobre Mouzinho Guterres, and their children.
Funeral arrangements are expected to be announced later.
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