Christodoulos was diagnosed last year with cancer of the liver and large intestine. He was treated in the U.S., but the cancer spread, making a liver transplant operation planned for last October impossible. He was reported to have refused hospital treatment in the final weeks of his life.
His coffin will lie in state in the Metropolitan Cathedral of Athens for three days, national television reported. The funeral will take place on the fourth day, which will be declared a day of public mourning, with national flags flying half-mast.
The archbishop was known as an outspoken conservative and defender of the church's role in state affairs, as well as a fierce critic of globalization and Turkey's bid to join the European Union.
Elected as church leader in 1998, the archbishop held a historic meeting with Pope John Paul II during his visit to Greece in 2001. He also met with the Catholic leader's successor Pope Benedict XVI at the Vatican in 2006 as part of efforts to end the Great Schism between the churches, dating back to 1054.
Holding degrees in law and theology from the University of Athens and a diploma in French and English philology, Christodoulos was secretary of the church's governing Holy Synod until 1974, when he was appointed metropolitan bishop of a diocese in central Greece, a position he held until his election as archbishop.
Christodoulos wrote several books on theology and morality.
Russia's Orthodox Church called the archbishop's death a huge loss for Orthodox Christianity.
"This is a great loss for the Hellenic people and the entire Orthodox Christianity," said Nikolai Balashov, head of the Moscow Patriarchy's inter-Orthodox relations.
He described the late archbishop as a "charismatic personality and true spiritual leader of Greece, who defended the Orthodox tradition in the context of globalization with great courage."
