Founder of the Secret Military Organization (later merged with the Home Army), commander of Kedyw and the Radosław Group during Warsaw Uprising.

He broke into the Polish II Corps in Russia commanded by general Józef Haller, in whose ranks he took part in the Battle of Kaniów.

During the Polish–Soviet War, he served as a military courier (he imported, among others, Józef Piłsudski's letters to Symon Petliura) and a counterintelligence officer.

In June 1940 he returned to the country and assumed the function of the Commander-in-Chief of TOW, an independent combat and subversive organization operating according to the guidelines of the Union of Armed Struggle.

In March 1943, after merging TOW with Kedyw he became the deputy head of the organization, colonel Emil August Fieldorf.

[1][4] After the initiation of the uprising, the unit seized major portions of the Wola suburbs, and subsequently defended it against German attacks carried out by troops under the command of SS Gruppenführer Heinz Reinefarth and Standartenführer Oskar Dirlewanger.

[note 1][6][7] On 11 August he was seriously wounded during the fighting On 15 September 1944, he sent his liaison officer to the east bank of the Vistula in order to establish contact with the troops of the First Polish Army.

In the absence of sufficient assistance on their part, on 20 September he ordered his decimated units to leave Czerniaków and pass through the sewers to Mokotów.

He left his soldiers a free hand - they could decide whether they would go to German captivity or leave the city with the civilian population.

Shortly before the order was signed, Mazurkiewicz was officially promoted to the rank of colonel, by general Tadeusz Bór-Komorowski, the commander of the uprising.

On 12 September captain Stanisław Sojczyński, the leader of the Underground Polish Army, sent an open letter to colonel Mazurkiewicz, in which he criticized him and called him a "traitor".

Later, the Stalinist authorities accused him that they were "secret underground meetings aimed at overthrowing the power of the Polish People's Republic".

[13] In August 1981, on the occasion of the 37th anniversary of the outbreak of the Warsaw Uprising, Telewizja Polska broadcast a documentary in which Mazurkiewicz talked about the real "Soviet assistance to insurgent units of the Home Army".

In the second half of the 1980s, general Jan Mazurkiewicz, then the highest-performing and functioning former Home Army officer in Poland, became part of the Social Committee for the Construction of the Warsaw Uprising Monument, which was unveiled on 1 August 1989, after his death.

[14] His funeral was attended by representatives of the highest state authorities, including generals Wojciech Jaruzelski and Florian Siwicki, professor Henryk Jabłoński and Jan Dobraczyński.

[15] Mazurkiewicz's first wife was Jadwiga,[citation needed] with whom he had three children, Stanislaw and Zofia, and an older son who died in infancy.

His wife and daughter were imprisoned by the Russians in the east of the country during the war, but his son escaped to England where he fought with the Polish Army based in Scotland before returning to Poland some years later.