During the First World War, aged fifteen, he fled Sedan and the German advance with his family to Marne, where he worked as an agricultural worker.

Sampaix then participated in the campaigns of the young communist party social struggles where he protested against the occupation of the Ruhr in 1923 and against the Rif war in 1925.

He made his first steps as a journalist in the local activist press by actively participating at L'Exploité de Reims, a communist weekly.

In November 1931, following a series of articles in favour of the mutinies in the army and calling for fraternization between workers and soldiers, Sampaix was arrested and sentenced to six, then ten months in prison.

[2] After the ban on L'Humanité on August 26, 1939, Lucien Sampaix participated in the clandestine re-publication of the communist daily, which led to his arrest by the French police in the December of the same year.

After having undergone multiple transfers, he managed to escape on December 25, 1940, and resumed contact with the clandestine editors of L'Humanité, but was once again arrested next year in March 1941.