Kasassoglou was born on December 1st 1908 in Athens. His father, Wassilis,
came from Polydorion in Asia Minor. His mother Eleni was a passionate music
lover. Georgios received his first violin lesson at the age of ten, in Edessa,
in the north of Greece.
He completed his secondary education at the age of sixteen and registered at the University of Athens to study classical philology. He took violin lessons with W. Skantzourakis and studied theory and composition in different music academies simultaneously, which was possible at the time. His teachers were: Lavrangas, Kontis, Warwoglis, Kalomiris and S. Spanoudi. After his studies at the University of Athens and at the music academies he registered for political science at the Pantios College.
In 1933 he became a high school teacher for music. Besides his teaching in high schools he endeavoured, wherever he was, to encourage musical activities.
In 1934 he married the pianist and singer Flora Papachristofilou, who had studied singing with the famous teacher Ghini and chamber music with Dimitri Mitropoulos, who, despite his exceptional talent, was still unknown at the time. After taking part in the Second World War on the Albanian front he composed in 1944 his orchestral piece Four Preludes on The Return from The Front which was often performed by the Athens State Orchestra.