Leys gained a considerable reputation at home and abroad and worked for an international clientele from Germany, France, England and Russia. He was made a knight in the French Legion of Honour and was awarded the Order of St. Michael by the king of Bavaria. Leys won a gold medal at the International Exhibition in Paris in 1855 for his historical painting "The Mass of Berthal de Haze" (Royal Museums of Fine Arts of Belgium, Brussels). Critics praised the high quality of his reconstruction of the past through costumes and architecture, the realistic poses and facial expressions, the rigorous drawing and the brightness of the colours. Leys won another gold medal in Paris in 1867. In 1862 Leys was created a baron by the Belgian King Leopold I.