Leonhard Bartlakowski grew up in a Polish family in Berlin. His father died when he was eight years old. Bartlakowski trained as a tailor. He volunteered for the Wehrmacht in 1936 but deserted in August 1939. After being put on a wanted list, he lived under a false name in various places. He was placed in a Soviet prisoner-of-war camp for a while, falling ill with tuberculosis. Bartlakowski was released and made his way to Rava Ruska (now Rava-Ruska, Ukraine) in 1941. He was deployed there as a German-Polish translator for the Gestapo, while also a leading member of a resistance group in Rava Ruska. As a translator, he gained advance knowledge of raids and deportations and warned Jews. In March 1943, he hid Romana Kessler, the sister-in-law of his friend Abraham Weinfeld, a Jewish pharmacist. He also took the doctor Stephanie Reicher into his one-room apartment. Later, she was joined by Weinfeld and his wife. Bartlakowski provided them with food from his workplace.
He returned to Berlin in 1946. Leonhard Bartlakowski died of tuberculosis at the age of 53. He was honored as Righteous Among the Nations posthumously in 1979.