Missori was born in Moscow in 1829, to a family of Bolognese origin, but soon moved to Milan, where he first proved his patriotic enthusiasm in the Five Days of Milan. An admirer of both Giuseppe Mazzini and Giuseppe Garibaldi, at the beginning of the Second Italian War of Independence he enrolled in the Hunters of the Alps corps, being assigned to the "Guide a Cavallo" ("mounted scouts") regiment. In 1859 he fought in some of the main battles on the Lombard front. In 1860 he was in the Expedition of the Thousand, and saved Garibaldi's life in the Battle of Milazzo (1860). In 1862, in behalf of Garibaldi, he created the army of volunteers from Reggio Calabria, Catanzaro, and Cosenza that eventually fought the Bersaglieri in the Battle of Aspromonte that same year. Between 1866 and 1867 he was again with Garidaldi in the Third Italian War of Independence, participating in several battles, including Bezzecca, Monterotondo, and Mentana.