Léon Mercier learned how to draw through a course by mail. His local newspaper, Le Courrier de l'Ouest, published his first comic in 1951, called 'À l'écu d'Or'. He then moved to Paris, where he made 'Terreur sur Braville' for the press. The Opera Mundi agency recognised him as a talented artist of animal comics and assigned him to do 'Félix le Chat', published in France-Soir. A year later, he moved to Mondial Press, for which he created 'Mambo'. This animal comic was first published in Le Parisien Libéré and was later reprinted in regional newspapers and pocket books. Léon Mercier has also worked for Pierrot ('Piaf et Pilou'), L'Intrépidé ('Goliath et Frisette') and Poucinet ('Poucinet'). He left the comics field in 1966 to start a career in advertisement, but returned in 1980 with 'La Plume aux Trousses' in Le Hérisson.