[3] In 1916 Hatzikyriakos joined the Provisional Government of National Defence under Eleftherios Venizelos, and was appointed as captain of the cruiser Georgios Averof, which he commanded during the Greek landing at Smyrna and the opening stages of the Greco-Turkish War of 1919–1922.

[3] Following the peace with Turkey (Treaty of Lausanne) he entered politics and was elected as a representative for Athens in the IV National Assembly, where he became a leading figure in the eventual abolition of the Greek monarchy and the establishment of the Second Hellenic Republic.

[3][4] He served as Minister for Naval Affairs in the Alexandros Papanastasiou cabinet (12 March 1924), until his resignation on 5 July 1924,[5] after which he retired from active service with the rank of rear admiral.

[3] Hatzikyriakos supported the June 1925 coup of general Theodoros Pangalos, and was appointed again as Minister for Naval Affairs in the new cabinet (serving also briefly as Foreign Minister during vacancies of the post in 26 June – 2 July and 26 October – 6 November) until his resignation on 8 January 1926.

[6] He served again as Minister for Naval Affairs in the 1933–35 Panagis Tsaldaris cabinet,[7] resigning due to his failure to prevent the fleet's participation in the failed coup attempt on 1 March 1935.