His heyday was during one of the most chaotic periods of modern Turkish history when governments changed sometimes annually under the shadow of the powerful military, and the country was beset by daily street violence and an economic slump.
He died of heart failure resulting from a severe respiratory tract infection, the state Anatolia news agency said, quoting the private Ankara hospital where he was treated.
Demirel served as prime minister on repeated occasions in the 1960s and 1970s and then again one final time in the 1990s before serving as head of state from 1993 to 2000.
President Recep Tayyip Erdogan said in a statement that Demirel had left "deep marks on Turkish political history" with his contribution to the country's development.
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Prime Minister Ahmet Davutoglu declared three days of national mourning for Demirel, with a state funeral ceremony to take place in Ankara on Friday and the burial of his body in his home Isparta region on Saturday.
Trained as an engineer, Demirel first went into politics in the early 1960s in the wake of the 1960 military coup that resulted in the execution of then premier Adnan Menderes.
He held together a government for some six years, a huge achievement by the standards of the time.