Léon Mignon studied under the sculptor Prosper Drion (1822–1906) at the Académie in Liège from 1857 to 1871. He was a particular admirer of the anecdotal sculpture of Léopold Harzé (1831–1893). His vocation as a sculptor of animal subjects began in Rome, where he studied on a grant from 1872 to 1876. He exhibited in Ghent (1874) and on several occasions in Paris (where he lived from 1876 to 1882) at the Salon des artistes français. He achieved prominence at the Exposition Universelle of 1878 in Paris with his bulls fighting in the roman countryside (Brussels, Museum of Modern Art). In 1880–81 he shared a studio with the Belgian sculptor Paul de Vigne, whom he had met in Rome. Mignon’s bull tamer (Liège, Parc Avroy) took the gold medal at the salon of 1880. In 1882 he settled in Brussels and in 1888 produced the labours of Hercules reliefs for the stairway of the palace of Charles de Lorraine. He sculpted several historical figures for the provincial law courts and a philosopher (1892) for the Université de Liège. As a sculptor of animal subjects, Mignon occupies a leading place in Belgian realist art. He also modelled busts of Belgian personalities as well as a statuette of the Belgian painter Hubert Bellis and an equestrian statue of Leopold II (1886; Brussels, Museum of Modern Art). His works are preserved in the Musée de l’art Wallon, Liège, and the Musée d’art Moderne, Brussels. He was completing a frieze for the Hôtel Somzée in Brussels when he died unexpectedly.
Leon Mignon was commissioned many times to create large Bronze sculptures for display at major cultural institutions, throughout the country.