In 1918, when Poland regained her independence, Zaleski proved to be a skilled diplomat and served in various posts in Polish embassies in Switzerland, Greece, Italy and was one of the Polish envoys to the League of Nations. After the May Coup d'État of 1926 he sided with the camp of Marshal Józef Piłsudski and, until 1932, held the post of minister of foreign affairs in two subsequent governments.