During World War II, Kyriakidis was rounded up with several other Greeks by German soldiers. When the soldiers came across his Berlin Olympic credentials, they released him. All the other men were shot.
Kyriakidis felt that God had spared him for a reason and after the war was over, decided - at age 36 - to re-enter the Boston marathon that he could not complete as a younger man. Despite warnings from doctors prior to the marathon that he could die if he ran, Kyriakidis entered and won the race on April 20, 1946, in record-breaking time: 2hr 29m 27s. His record would stand until the late 1960s. After finishing the race, Kyriakidis comments to the US media were: "Please, don't forget my country!
After his victory, Kyriakidis campaigned for humanitarian aid for Greece whose economy had been wrecked by war, occupation and civil conflict. He returned to Greece to a hero's welcome bringing with him aid worth $3,000,000.
Kyriakidis also competed in the 1948 London Olympics finishing 18th, however, his mark on history had already been made.