He served in the Crimean War, in Italy, and in Mexico. For bravery at the battles of Magenta and Solferino, he was elevated to brigadier general. During the Franco-Prussian War he was Commander-in-Chief of the French Seventh Army Corps. After the first defeats on the Alsace border, 7th Corps retreated and became part of Marshal Patrice de Mac-Mahon's frontline Army of Châlons. He was taken prisoner at the Battle of Sedan. After his return to France, Douay led his Fourth Army Corps against the Paris Commune. He was first to enter Paris, 22 May 1871, and saved the Louvre from destruction.