He was born in Corfu in c. 1861,[2] a descendant of a branch of the Albanian Dushmani family that had emigrated to the island in the 15th century; he is the elder brother of Sofoklis Dousmanis and grandson of Antonio Dusmani.

[2] Promoted to Lieutenant in 1886 and Captain in 1890, he participated in the Greco-Turkish War of 1897 as an officer in the staff of the Army of Thessaly under the Greek Commander-in-Chief, Crown Prince Constantine.

[2] During the First Balkan War of 1912–1913 against the Ottoman Empire, he was chief of operations for the main Greek force, the Army of Thessaly, again under Crown Prince Constantine.

[2] In early 1914 he was appointed Chief of the General Staff Service, but resigned in November after a quarrel with Prime Minister Eleftherios Venizelos over the issue of Greece's entry into World War I.

[2] Venizelos favoured siding with the Entente Powers, especially Britain, for the upcoming Gallipoli Campaign while Dousmanis, a believer in the victory of Germany, advocated neutrality.