Born on 23 October 1861 at Levadeia, Ioannou entered the Hellenic Military Academy and was commissioned as a 2nd Lieutenant in the Engineers on 25 July 1884.

[2] He was named as the commanding officer of the newly raised 9th Infantry Division in 1913, and commanded it until 1916, when he joined the Venizelist Movement of National Defence in Thessaloniki, which, in opposition to the royal government in Athens, entered World War I on the side of the Entente Powers.

Ioannou was tasked with the formation of the Archipelago Division, drawn from the inhabitants of the Aegean islands.

He led his division to victory at the Battle of Skra-di-Legen in May 1918, and participated with it in the general Allied offensive of September 1918, which broke the German-Bulgarian front.

[2] The Greek writer Stratis Myrivilis, in his anti-war novel Life in the Tomb, which describes life on the Macedonian Front based on the author's own experiences as a soldier in the Archipelago Division, gives a portrait of Ioannou, under his popular nickname Balafaras: a slightly buffoonish but larger-than-life man, who likes to demonstrate his personal bravery by refusing to take cover or wear a helmet while visiting the trenches in full uniform, and whose more foolhardy impulses have to be restrained by his aides and the French high command.