Kammala jumla mai zuwa: Bayan karɓar hukunci mai sauƙi a ƙasarsa na dakatar da watanni shida, Brunet ya koma sojojin Faransa a watan Fabrairun 1870, tare da ɗan rashi kaɗan a cikin tsofaffi. A lokacin yakin Franco-Prussian na 1870-1871 ya bambanta kansa a yakin da aka yi a
Spicheren, Mars-la-Tour da kuma Gravelotte. An kama shi a zaman fursuna a Siege na Metz. Bayan yakin, Brunet ya taka muhimmiyar rawa a matsayin memba na Sojojin Versailles a cikin murkushe Paris Commune. Ya ziyarci Royal School of Military Engineering a Burtaniya a watan Agusta 1871, kuma daga baya a wannan shekarar an sanya shi jami'in Légion d'honneur kuma an sanya shi a matsayin mai taimakawa sansanin Ministan War, Ernest Courtot de Cissey.