A. G. Xydis was the son of George Xydis and Alexandra Dragoumi, and the grandson of Stefanos Dragoumis, who served briefly as Greek Prime Minister in 1910. Born in Liverpool, he studied law, political science and art history in Paris and Munich. In 1904 he joined the Diplomatic Corps, serving successively in Athens, Morocco, Casablanca, Canberra, London and Damascus. In the 1950s he served in London alongside George Seferis, with whom he shared a great friendship and whose work The Political Diary (1979, 1985) he edited.

Xydis was an important art critic and a founding member of the Association of Greek Art Critics, which he served as Secretary and President for many years. During his life he assembled a significant collection of engravings and paintings, which he donated to the Macedonian Museum of Contemporary Art. Part of his political archive was donated to the Contemporary Social History Archives. In addition to publishing the magazine Τετράδιο(1945-1947), Xydis wrote numerous articles and monographs on Greek artists (Theotokopoulos, Kapralos, Parthenis, Bouzianis, Tsarouchis, Engonopoulos, Chatzikyriakos-Ghikas etc.), along with studies on modern Greek art (Propositions on the History of Modern Greek Art, 1976), while overseeing important exhibitions in Greece and abroad. He also authored a study on the Cyprus Dispute (1993). His work and activity changed the face of Greek art criticism and contributed to the configuration of modernist art in Greece from 1940 to 1990.