Frantzis, aka Sfrantzis, was born into nobility in Constantinople, in 1401. In 1423, he accompanied Emperor John VIII Palaeologus to Peloponnesus where he met Constantine Palaeologus, the future emperor. There, he took part in several battles to recover lands for the Despot of Mystras and was injured in one such battle at Patra and taken prisoner. After Frantzis was freed, he became governor of Patra and took part in negotiations on behalf of the despot. In 1438 he married into the Palaeologus family eventually fathering four children.
When Constantine Palaeologus became Byzantine Emperor in 1449, Frantzis returned to Constantinople becoming a close aide of the new emperor who entrusted him with several important diplomatic missions. When Constantinople fell on May 29, 1453, Frantzis and his entire family was captured and taken to Sultan Mehmed II who personally killed Frantzis' son and took one of his daughters into his harem. Frantzis, himself, managed to buy his freedom the following year and left for Mystras.
By 1457, Frantzis was living in Lefkada and the following year in Corfu where he entered a monastery. His wife entered a nunnery. While in the monastery, Frantzis wrote the Chronicon - the history of the time period 1258 - 1477, including the Fall of Constantinople which he witnessed first-hand.
Frantzis died in 1480.