 Gacek served as a member of the Polish Senate for the Civic Platform party between 2005 and 2007.In 2007 she became a Member of the European Parliament and sat with her colleagues in the EPP-ED group, serving, amongst others, on the Committee on Civil Liberties, Justice and Home Affairs and the Delegation for Relations with the USA.From 3 February 2011 to 30 November 2014 she was the Permanent Representative of the Republic of Poland to the Council of Europe.