Born in Miastków (in Garwolin District) on the 22nd of March, 1891. He completed secondary school in Siedlce and studied at the Department of Chemistry of the Lviv Polytechnic and at the Agricultural Study of the Jagiellonian University. From his youth he was connected with the Socialist movement and was active in the Combat Organization of the Polish Socialist Party and the Polish Socialist Party - Revolutionary Faction. After the outbreak of the First World War, he helped to form, and then headed, the Polish Military Organization (POW). In the middle of the year 1915 he was assigned to Brigade I of the Polish Legions and then detailed back again to the POW, where he held the most responsible positions; for instance, he headed the POW General Headquarters No. 3, which operated in the area of Russia, Belarus, and Ukraine. He belonged to the ‘Convention of Organization A’, a body commonly considered the leadership of the whole Piłsudski’s camp. Following the rebirth of independent Poland, Miedziński served in Polish military intelligence and counter-intelligence; he was an officer for special tasks of the Minister of Military Affairs and the Deputy Aide-de-camp General of the Commander-in-Chief. He was among the most trusted collaborators of Józef Piłsudski, and from 1937 on - of Edward Rydz-Śmigły. For many years he also held seats in Polish Parliament on behalf of the Polish People’s Party ‘Piast’, Polish People’s Party ‘Wyzwolenie’, and the Nonpartisan Bloc for Cooperation with the Government (BBWR); in 1927-1929 he served as the Minister of Post and Telegraphs, too. He was the Deputy Marshal of the Sejm and then - in 1938-1939 – the Marshal of the Senate. He helped to draft the political manifesto of the Camp of National Unity (OZN). He was very active as publicist, writing for “Kurier Poranny” and “Głos Prawdy”, and in 1929-1938 was the editor-in-chief of “Gazeta Polska”. From 1939 on, Miedziński lived in exile and in 1947 settled down in England. He died in London on the 8th of May, 1972. His principal work is Zbiór znaczących artykułów Wczoraj - dziś -jutro (Warsaw, 1938).