Johannes Guillaume Christianus Andreas (Jan) Marijnissen (Oss, October 8, 1952) is a Dutch former politician. He was a member of the House of Representatives of the States General from 1994 to 2010 on behalf of the Socialist Party. From 1988 to 2015, he was party chairman of the SP, and from 1994 to 2008, he was parliamentary group leader and political leader of his party.