Born in 1919 to Greek parents in Tuzla, near Constantinople, Maropoulos came to Greece with his family at age 3 during the population exchanges after the Greco-Turkish War in 1922. Having settled in Kalamata, at age 12 he joined the local football club Prasina Poulia, the "Green Birds". When his parents moved to Kalogreza in the Athens area, he signed for Ethnikos Kalogreza. In 1934, he and Tryfon Tzanetis were spotted by AEK Athens who placed them in their youth team. In 1936, he was promoted to the first team. He played in AEK's attack and he was the fear and terror of the opposing goalkeepers with his terrible shot. The slogan ""Maropoulos, you cannot!" (Greek: "Δεν μπορείς Μαρόπουλε!")" was originally chanted by the opponent's fans, but later on came to be a chant of the fans shouted at him to make him bitter or stubborn to make him tear the opponent nets. Led by Maropoulos, alongside players like his fellow, Tryfon Tzanetis and Kostas Negrepontis, AEK won their first two Greek Championships in 1939 and 1940 - the first domestic double by a Greek club. Unfortunately, the glory years of AEK and Maropoulos were interrupted by World War II. During Τhe Occupation, he actively participated in the Union of Greek Athletes. The objectives of the UGA were to maintain athletic activity (albeit substandard) and to support athletes in difficulty due to illness or hunger. Maropoulos did continue his career after the war, playing until the early 1950s. Overall, he played in 144 matches and scored a total of 89 goals.