In 1912 he entered the KTSSN, a Galicia-based confederation of all the political factions supporting Austria-Hungary as the only state to be able to reunite and liberate Poland after roughly a century of partitions.
After the foundations for the Polish Secret State had been laid, in 1941 Jankowski became the Director of Labour and Social Care (a de facto minister) of the Government Delegate's Office at Home.
After Jan Piekałkiewicz was arrested by the Gestapo in February 1943, Jankowski replaced him as the Government Delegate at Home, under the formal rank of the deputy Prime Minister of Poland.
During the fighting in Warsaw, he remained close to the headquarters of the Armia Krajowa, but lost any contact with most of the cells of the Government Delegate's Office in other parts of Poland.
In addition to the Virtuti Militari (5th class) he received for his service in the Warsaw Uprising, in 1995 Jankowski was posthumously awarded the Order of the White Eagle.