In 1989, at the age of 26, he was appointed assistant professor of Classical Studies and Anthropology at the University of Manitoba in Winnipeg, Canada, where he taught a wide range of subjects and received two teaching awards.
He has excavated at various archaeological sites in Greece and Ukraine, including Mycenae, Epidavros, Ancient Corinth, Naxos, Ithaca, Oropos and Olbia (now Berezan) in the Black Sea.
His excavations in Iklaina brought to light an important center of Mycenaean civilization with Cyclopean walls, frescoes, paved streets, and the oldest record of Linear B of Mainland Greece.
He has given hundreds of lectures on Greek archaeology issues in Canada, United States, Greece, Germany, and the UK.
[16] Cosmopoulos has published 16 books and more than 100 articles and scholarly papers on the archaeology, culture, and socio-political history of ancient Greece.