Marek Siwiec was born in Piekary Slaskie in southern Poland and graduated from the Department of Solid-State Physics at Academy of Mining and Metallurgy in Cracow in 1980, and the Post-Graduate Journalist Studies in Warsaw in 1988. From 1990-1991, Siwiec was an editor-in-chief of the Trybuna daily. In 1991 he became a member of Polish Parliament (Sejm). During this time he also served as a member of the Democratic Le Alliance (SLD) Parliamentary Caucus, a member of the Parliamentary Committee on Culture and Media, and for parliamentary friendship groups: Poland-Columbia and Poland-South Korea. From 1993 he was a press spokesman of the SLD Parliamentary Caucus. In 1993 Siwiec became a member of the Parliamentary Assembly of the Council of Europe. In the years 1993-96, he was a member of the National Broadcasting Council. In 1996 he became a secretary of state in the Chancellery of the President of the Republic of Poland and served as the head of political strategy staff. On February 19, 1997, he was nominated head of the National Security Bureau and he held this position until he was elected as a member of the European Parliament in the first ¨European¨ elections in Poland in 2004. At the beginning of his term, he was responsible for the Ukrainian delegation.
Siwiec was a vice-president of the European Parliament between 2007 and 2009. He was reelected MEP in 2009, gaining 64,976 votes. He was a full member of the Parliamentary Committee on Foreign Affairs and a substitute in the Committee on Internal Market and Consumer Protection. He also served as a coordinator of the Group of the Progressive Alliance of Socialists and Democrats for the Euronest Parliamentary Assembly. He is a member of the Board of Yalta European Strategy foundation (YES) and President of the European Friends of Israel. In December 2012 he withdrew from the Democratic Left Alliance (SLD) and in October 2013 he co-founded the new centre-left party “Twój Ruch” of which he became vice-president.