However, his naval career was very brief; beginning in 1935, he worked for various Greek newspapers, writing articles on world politics, economics and geopolitics.
During World War II, and after the fall of Greece to the Nazis, he was active in the Greek Resistance, joining the left-wing National Liberation Front (EAM) and serving as an officer in the Greek People's Liberation Navy (ELAN), the naval branch of the more famous Greek People's Liberation Army (ELAS).
He was also involved in politics, being elected in the "National Council" that EAM had set up, representing Edessa.
As a war correspondent, Grigoriadis covered many important 20th century conflicts, such as the Vietnam War and the Prague Spring, and many of his articles and publications about strategy and politics were published in Greek and international military reviews.
His writing style combined historical accuracy with journalistic flavor, and this was a major factor in the success of his works.