Analysis of the case of a Portuguese diplomat, João Chagas, who, during the First Republic, and by resorting to the conditions available to him as representative of his country, surpassed the mere negotiating role attributed to diplomacy to conduct national politics, succeeding in changing the international statute of Portugal in the Great War. The article describes the internal and external situation of Portugal in political, geopolitical and geostrategic terms, the conflict between Portuguese and British interests, the activity of Portuguese diplomats in London, Berlin and Paris, and, finally, the work of João Chagas