Xanthos was born in 1772 on the island of Patmos in the Dodecanese. He migrated first to Trieste and later - 1810 - to Odessa, Russia for business purposes but, while there, became acquainted with Athanasios Tsakaloff and Nikolaos Skoufas. The three men came up with the idea of founding a secret organisation to prepare the ground for Greek independence and Filiki Eteria was born in 1814.
Xanthos became the treasurer and chief contact man of the organisation. His efforts to pursuade Ioannis Kapodistrias to take a leadership role in the organisation failed as the latter adopted a more realistic approach as to the chances of a Greek revolt against the Ottoman Empire. Xanthos, instead, offered the position to Alexandros Ypsilantis who started the Greek Revolution in Moldavia in March of 1821.
In 1837, Xanthos returned to Greece, now an independent state. He was appointed to a minor administrative post but was shortly dismissed. In 1845, he published his memoirs about the Friendly Society - the only one of the three founders to do so. He spent the rest of his life in poverty and died in Athens on November 29, 1851.