Johannes Guillaume Christianus Andreas "Jan" Marijnissen is a retired Dutch politician of the Socialist Party (SP).

The Socialist Party is a democratic socialist and social democratic political party in the Netherlands. Founded in 1971 as the Communist Party of the Netherlands/Marxist–Leninist, the party has since moderated itself from Marxism–Leninism and Maoism towards democratic socialism and social democracy. The SP has also been described as left-wing populist, far-left and Eurosceptic, and is an advocate of Dutch republicanism.