Charles Félix César Longuet (French pronunciation: [ʃaʁl feliks sezaʁ lɔ̃ɡɛ]; 14 February 1839, Caen – 5 August 1903, Paris) was a journalist and prominent figure in the French working-class movement, including the 1871 Paris Commune, as well as a Proudhonist member of the General Council of the First International or International Working Men's Association (1866–67, 1871–72).

[4] Longuet participated in the Paris Commune of 1871 and, after its defeat, moved to England as a refugee where he met Karl Marx.

Longuet married Marx's eldest daughter, Jenny, on 2 October 1872 in London (in a civil ceremony).

Here he took a position as an editor of La Justice, a radical daily newspaper founded by Georges Clemenceau.

[7] His wife and children joined him in February 1881, the family settling in the town of Argenteuil, near Paris.