Jan Marinus Wiersma (born 26 August 1951 in Groningen) is a Dutch politician and from 1994 to 2009 Member of the European Parliament. He is a member of the Labour Party, vice-chair of the Party of European Socialists group, and sits on the European Parliament's Committee on Foreign Affairs.
He was also a member of the Subcommittee on Security and Defence, a substitute for the Committee on Transport and Tourism, a member of the delegation to the EU - Romania Joint Parliamentary Committee, and a member of the delegation to the EU - Moldova Parliamentary Cooperation Committee.