Jan Joniuk lived in Warsaw during World War II. Father of Leokadia (married name Michalska), Eugenia (married name Bartosiak) and Zofia (married name Wycech). Together with his daughter Eugenia he sheltered six people of Jewish origin with the following surnames: Michelson, Jomtow and Walerschtein.

Jan Joniuk and his daughter Eugenia were awarded the title Righteous Among the Nations in 1983.