 Graduating from a Tradesmen's Association Commercial School in Warsaw, Mijal became active during World War II, collaborating with Paweł Finder, Marceli Nowotko and Bolesław Bierut.He served as Mayor of Łódź, chief of the Presidential Chancellery, chief of the Bureau of the Council of Ministers, Minister of Communal Economy, and director of the Investment Bank.He was a long-time member of the CC of the Polish Workers' Party and then the PUWP.