At the end of the Second Italian War of Independence in 1859, he became commander of the engineers of the French occupation forces in the Papal States, serving in that role for five years.

He was able to escape capture when Metz capitulated and offered his services to the Government of National Defense, which sent him to the north of France to serve as military governor of Lille.

Despite the greater experience and much higher strength (45,000 men) of Prussian General Edwin Freiherr von Manteuffel′s army, which was moving up towards Amiens, Farre did not hesitate to block Manteuffel′s path.

The memory of Farre′s collaboration with General Faidherbe during the Franco-Prussian War had won Farre the sympathies of the political left of the French Parliament.

When Charles de Freycinet retired, Farre kept the War portfolio in the reconstituted cabinet created on 23 September 1880 under the chairmanship of Jules Ferry.

To meet the needs of the expedition, Farre as Minister of War initiated a system of reinforcements given the name "small packages," and from the political right to the far left, he was accused of jeopardizing the mobilization capability of the French Army.