He was a professor at the Institute of Philosophy of the University of Warsaw and the director of its Department of Social Philosophy. Marek Siemek was a disciple of Bronisław Baczko, one of the main representatives of the Warsaw School of the History of Ideas. Fellow of Collegium Invisibile.
On 10 February 2006 he received doctorate honoris causa of the University of Bonn.
Marek Siemek had one son, currently residing in the United States.