Marek Maciej Siwiec (born 13 March 1955 in Piekary Slaskie) is a Polish politician and journalist.

During his tenure in European Parliament he also served as a coordinator of the Group of the Progressive Alliance of Socialists and Democrats for the Euronest Parliamentary Assembly.

In 2016 he was appointed as a Chief Executive Officer of Babi Yar Holocaust Memorial Center, a non-governmental organization with its mission to respectfully commemorate the victims of the Babi Yar and to promote the humanization of mankind through the memory preservation and study of the history of the Holocaust.

During presidency campaign in 2000 a film was published revealing Marek Siwiec, then the chief of National Security Bureau, allegedly parodying a gesture of then pope John Paul II (making a cross sign in the air on arrival).

On 26 March 2009 Institute of National Remembrance, after its own investigation, decided about discontinuance of the proceedings due to lack of evidence about collaboration.