Pelloux was born in La Roche-sur-Foron, Savoy, then part of the Kingdom of Sardinia. Entering the army as lieutenant of artillery in 1857 he gained the medal for military valour at the Battle of Custoza in 1866, and on September 20, 1870, commanded the brigade of artillery which battered the breach in the wall of Rome at Porta Pia, which enabled Bersaglieri soldiers to enter Rome and complete the unification of Italy. He entered the war office in 1870, and in 1880 became General Secretary, in which capacity he introduced many useful reforms in the army.