Fornalska was born in Fajsławice to a family of communist activists. From 1918, she was a member of the Social Democracy of the Kingdom of Poland and Lithuania and the Russian Communist Party (bolsheviks) as well as the Communist Party of Poland. From July–December 1918 she worked at orphanages in Saratov and Petrovsk.
In January 1920, Fornalska returned to Poland and worked for the Provisional Polish Revolutionary Committee together with her brother Aleksander. Later, she studied at the Sverdlov Communist University and the International Lenin School in Moscow.
Fornalska was arrested and imprisoned several times for her communist activity in Poland in the 1930s. After being released in 1939, she went to the Soviet Union, where she worked with other exiled Polish communists. In the spring of 1942 she was parachuted into Poland, then occupied by Nazi Germany, in order to organize the communist resistance against the occupation. She was elected to the Central Committee of the newly formed Polish Workers' Party and worked as one of the editors of the party's newspaper, Trybuna Wolności.
Posthumously, Fornalska was awarded the Order of the Cross of Grunwald, 1st class, in 1948.
- Jerzy Eisler, Siedmiu wspaniałych. Poczet pierwszych sekretarzy KC PZPR [The Magnificent Seven: first secretaries of the PZPR], p. 55. Wydawnictwo Czerwone i Czarne, Warszawa 2014, ISBN 978-83-7700-042-7.
- Michałowska-Walkiewicz, Eva. "Małgorzata Fornalska - Z listy osób wyklętych". Dziennik Polonijny. Retrieved 27 February 2018.