Klontzas was born in
Heraklion. His father Andreas Klontzas was associated with the cultured circles of Cretan society. Georgios inherited several houses from his wealthy parents, and was also given the Greek Orthodox church of St Mark in the city of Candia (Herakleion). In 1566, he married Ergina Pantaleos, the daughter of a priest named Emmanuel Pantaleos. Ergina and Georgios had three sons, Loukas, Maneas, and Nicolaus, all of whom were painters. He later remarried to Lia Vitzimanopoula, with whom he had a fourth son. By 1564, Klontzas was a freelance painter working all over Candia. Two years later, he was hired to assess an icon by
Domenikos Theotokopoulos. Records indicated two paintings (now destroyed) were commissioned in 1586. One depicted the healing of the paralyzed individual. The other painting was for the Catholic church of the welfare institution of St Anthony in Candia. By 1587, the painter was commissioned by the Bishop of Karpathos. His name was Ioasaph Avouris. Around that time he purchased his workshop. It was located at the square of Saint Mark in the center of Candia. Klontzas became very popular his patrons included Orthodox and Catholic institutions, Greek bourgeois, and Venetian noblemen. A Venetian nobleman
Francesco Barozzi born in Herakleion commissioned Klontzas to create two illuminated manuscripts for
Giacomo Foscarini. Foscarini was the administrator and tax collector of Crete. The manuscripts contain the
Oracles of Leo the Wise. A third, more complex, leather-bound manuscript was completed during the 1590s. It contains 217 paper folios with over 400 miniature drawings. Klontzas' signature is at the end of the book. The textual frame is proved by the seventh-century
Apocalypse of Pseudo-Methodius. It starts with the
Expulsion from the Garden of Eden and ends with the
Last Judgment. The codex features Biblical and prophetic texts ensconced with Byzantine and Ottoman history. The pictures stylistically resemble Venetian and Flemish icon paintings. Another lesser-known artist from Crete was Markos Bathas. He also completed a manuscript in a similar style. The painter was probably associated with the poet
Antonios Achelis. He was the author of the
Siege of Malta (1570) dedicated to Francesco Barozzi. Klontzas's visual motifs and Achelis's writings share a connection. Klontzas created a book of prophecies which he gave to his son Loukas in 1597. Klontzes died in 1608.{{cite web ==All Creation Rejoices In Thee==