Maciej's father was Władysław Jan Grabski, a renowned writer who wrote historical novels on the History of Poland. He was the second son of Władysław Grabski, noted politician, independence activist and economist who served as Prime Minister of Poland for two non-consecutive terms plus was the author of the currency reform which contained hyperinflation and stabilized the zloty exchange rate until 1939, and his wife Katarzyna Lewandowska, a daughter of a wealthy landowner of szlachta descent. Kidawa-Błońska's paternal grandmother was painter Zofia Wojciechowska-Grabska, only surviving child of Stanisław Wojciechowski, who served as President of Poland from 1922 to 1926 after he was ousted by the May Coup d'État led by Marshal Józef Piłsudski, and his wife Maria Kiersnowska, who served as the First Lady during her husband's presidency. She was previously involved in the underground work and later became a courier for the Polish Socialist Party for the call for Polish Independence.