Jules Guesde played a central role in the history of French and European socialism. He set up the first working-class party in modern history, the French Workers’ Party (POF) that was created between 1879 and 1882, and he held discussions with Karl Marx in London in 1880. Guesde was the main founder, with Jean Jaurès, of the unified French Socialist Party in 1905. He also helped introduce and popularize Marxist thought in France.

Yet the legacy of Guesde is controversial. In the name of a rigid understanding of class struggle, Guesde refused to support the campaign for the release of Captain Alfred Dreyfus, a Jewish army officer who was falsely accused of treason and imprisoned in 1895. Guesde took this position not out of antisemitism, but rather because Dreyfus was a soldier, at a time when memories of the repression of the 1871 Paris Commune by the French military were still vivid.

Guesde combined his Marxism with a very pragmatic approach to politics that earned him accusations of opportunism. He became a minister in the French government after the outbreak of war in 1914 and was reviled by those who opposed the war. After 1918, he chose to remain with Léon Blum in the Socialist Party, rejecting the terms of the Bolsheviks for membership of the new Communist International.