A legal advisor to King Constantine I, Streit was Minister of Foreign Affairs from 1913–14, on the eve of World War I.
During this period, Streit was active in supporting the Greek population in Macedonia, which was still under the hegemony of the Ottoman Empire.
In addition to his academic post, Streit also served as an advisor to the Greek Foreign Ministry and in 1910, during the Ministry of Eleftherios Venizelos, he was appointed Greek Ambassador to the Austro-Hungarian Empire serving in Vienna.
In March 1913, Venizelos appointed Streit as Foreign Minister, despite his perceived inclination towards the Triple Alliance of Germany, Austria-Hungary and Italy.
In June 1917, with the government of Venizelos having overcome King Constantine's favored policy of neutrality in World War I and Greece actively joining the war on the side of the Triple Entente, the King abdicated his crown in favor of his second son and left Greece for exile in Switzerland.