The former head of state had been hospitalised with breathing difficulties since 27 August at the Hospital de Santa Cruz, in Lisbon.
Sampaio was in the Algarve, but after experiencing respiratory difficulties, and "given his history of being a heart patient", he was transferred to Lisbon.
Jorge Sampaio, 81 years old, was President of the Republic for two terms, between 1996 and 2006.
In 1989 he was elected leader of the Socialist Party and at the same time he was elected mayor of Lisbon, having been re-elected in 1993.
After serving as President of the Republic, he was appointed in 2006 by the Secretary General of the United Nations Special Envoy for the Fight against Tuberculosis and between 2007 and 2013 he was the UN High Representative for the Alliance of Civilizations.
He currently chaired the Global Platform for Syrian Students, founded by him in 2013 with the aim of contributing to respond to the academic emergency that the conflict in Syria had created, leaving thousands of young people without access to education.
Jorge Fernando Branco de Sampaio held, throughout his life, the highest political positions in the country.
He began his journey, while still a student, as one of the protagonists, at the University of Lisbon, of the academic crisis of the early 1960s, which generated a long and widespread movement of student protest against the Estado Novo, until 25 April 1974.
Later, he was secretary general of the PS (1989-1992), president of the Lisbon City Council (1990-1995) and President of the Republic (1996 and 2006).