Katsotas was born in the village of Stamna in Aetolia-Acarnania in 1896. He graduated from the Hellenic Army Academy in 1916 as an Infantry 2nd Lieutenant, and served in the Army until his voluntary retirement in 1929. Following the outbreak of the Greco-Italian War in 1940, he was recalled to service, and fought in the Albanian front as a regimental commanding officer with the rank of lieutenant colonel. Following the German invasion of Greece in April 1941, he fled the country and joined the forces of the Greek government in exile in the Middle East. He assumed command of the 1st Greek Infantry Brigade, with which he fought in the Second Battle of El Alamein.