Jean-Laurent-Frederick Longuet (Johnny) (1876–1938) was a French socialist and Karl Marx's grandson.
Son of Charles and Jenny Longuet. French lawyer and Socialist who in the First World War and founder and editor of the newspaper Le Populaire. He was a pacifist, but also supported war credits during the course of the First World War. At the Strasbourg Congress in 1918 his policy was adopted by the majority of the French Section of the Workers' International (SFIO) socialist party. After the Tours Congress of 1920 where the Communists gained the majority he supported the minority and joined the centrist Two-and-a-half International (the Vienna Union). He criticized the League Against Imperialism created in 1927 and supported by the Comintern.
- ”The sessions which adopted the pro-Zionist resolution was presided over by Emile Vandervelde, Belgian Socialist leader and friend of Zionist. Among those who gave their approval to the resolution were Leon Blum, French-Jewish Socialist; Jean Longuet, grandson of Karl Marx; Pierre Renaudel; and M. Turati, Italian Socialist leader (”Socialist International Urges Britain to Facilitate Jewish Immigration, Colonization,” Jewish Telegraphic Agency, August 7, 1930).
- “Jean Longuet, grandson of Karl Marx, father of modern Socialist, announced himself as a Zionist in a speech to a Zionist group here” (The Sentinel (Chicago), May 30, 1935, p. 29).