After his art studies at the Academy of Fine Arts in Lille, then at the School of Fine Arts in Paris, Agathon Léonard settled permanently in Paris where, after exhibiting at the 1868 Salon, he joined the Society of French Artists in 1887, then the National Society of Fine Arts in 1897.
Very involved in the Art Nouveau style, he exhibited numerous pieces (medallions, bronze statuettes and ceramics) finely worked, especially at the 1900 Universal Exhibition in Paris where he presented the famous "Jeu de l'écharpe" in Sèvres porcelain. He also works in marble, quartz and ivory. His works are mainly centered around the human figure, especially female.
In 1901, he was named Rosati of honor.