In the Italian War of 1859 he commanded the artillery, and by his action at the battle of Solferino materially assisted in achieving the victory. In September 1866, having in the meantime become aide-de-camp to Napoleon III, he was dispatched to Venetia to hand over that province to Victor Emmanuel. In 1869, on the death of Marshal Niel, General Leboeuf became minister of war, and earned public approbation by his vigorous reorganization of the War Office and the civil departments of the service. In the spring of 1870 he received the marshal's baton.
On the declaration of war with Prussia, Marshal Leboeuf delivered himself in the Corps Législatif of the historic saying, "So ready are we, that if the war lasts two years, not a gaiter button would be found wanting." It may be that he intended this to mean that, given time, the reorganization of the War Office would be perfected through experience, but the result inevitably caused it to be regarded as a mere boast, though it is now known that the administrative confusion on the frontier in July 1870 was far less serious than was supposed at the time. Leboeuf took part in the Lorraine campaign, at first as chief of staff (major-general) of the Army of the Rhine, and afterwards, when Bazaine became commander-in-chief, as chief of the III Corps, which he led in the battles around Metz. He distinguished himself, whenever engaged, by personal bravery and good leadership. Shut up with Bazaine in Metz, on its fall he was confined as a prisoner in Prussia.
On the conclusion of peace be returned to France and gave evidence before the commission of inquiry into the surrender of that stronghold, when he strongly denounced Bazaine. After this he retired into private life to the Chateau du Moncel near Argentan, where he died in 1888.