Fleeing the royalist reaction of 1799, when Napoleon's republican forces were routed from Italy, the 15-year-old Filangieri sought refuge in France, where he entered the military academy in Paris. He joined the French Army in 1803 and was made captain at the Battle of Austerlitz (1805). Recalled into the Neapolitan Army, he fought in Spain, where he distinguished himself as much by his personal duels as by his military success. He played a brilliant role in the Bonapartist Gen. Joachim Murat's unsuccessful campaign against Austria in 1815; he was seriously wounded at Panaro. During the Neapolitan insurrection of 1820 he supported the constitutionalist party and fought the Austrians, who overthrew the revolutionary government and restored the monarchy (March 1821). Filangieri was dismissed, and he retired to Calabria, where in 1819 he had inherited the princely title and estates of Satriano.

In 1831 Ferdinand II, king of the Two Sicilies, recalled him to command the army. In his suppression of the 1848 Sicilian revolution, he bombarded and captured Messina (September) and besieged and took Catania, where his troops committed many atrocities; by May 1849 he had subdued the entire island. Named duke of Taormina, he governed Sicily until 1855.

Filangieri became Neapolitan minister of war and president of the council under Francis II (1859). He soon resigned, however, after Francis' rejection of his proposal to grant a popular constitution and to ally Naples with France and Piedmont against Austria. In 1860 he refused to fight the revolutionary leader Giuseppe Garibaldi in Sicily and retired to private life.