Niel managed to carry out this delicate and difficult task with as much success as could be expected, and he directed siege operations at the Battle of Malakoff. His reward was the grand cross of the "Légion d'honneur". From 1855 to 1859 Niel was employed at headquarters and also served in the French Senate. In the war against the Austrians, Niel commanded the IV Corps and took part in the Battle of Magenta and the Battle of Solferino. Niel was made a marshal of France on the field at Solferino.