Demetrios Aiginitis studied in Varvajkeios School and then in the University of Athens. He then studied in Paris Astronomy for three years in a State Scholarship. In 1890, he came back to Greece and was appointed the Director of the Observatory of Athens until his death. He founded the meteorological and seismological divisions of the Observatory and managed for the astronomical division to receive expensive new instruments via donations.
Aiginitis was also active in politics, becoming the Minister of Education twice. He helped create the Academy of Athens, was instrumental in the organization of the University of Thessaloniki and helped institute the Gregorian calendar in Greece. He was a member of various international scientific bodies and wrote numerous books and papers.