Jean Pennes was born in France in 1894. Although Pennes did not have any formal art training by sixteen his cartoons were being accepted by French newspapers. Pennes, who signed his work J. Sennep, freelanced until being called up into the French Cavalry on the outbreak of the First World War.

After the Armistice Sennep worked as a journalist and cartoonist. His work appeared in most of the leading French newspapers and eventually he became the senior cartoonist at Le Figaro. During the 1930s and 1940s Sennep's attacks on Adolf Hitler and his fellow Nazis rivalled those of David Low in Britain.