A graduate of the Turin Military Academy, La Marmora entered the army in 1823 and first distinguished himself in the Italian wars of independence against Austria, especially at Borghetto and Peschiera (May 1848). He also commanded the Sardinian forces in the Crimea (1855). On Aug. 5, 1848, he rescued the Sardinian king Charles Albert from Milanese revolutionaries, who had resented the King's armistice with the Austrians. He was promoted to general in October and served as minister of war until November; he later suppressed an insurrection at Genoa (April 4–5, 1849). As minister of war again until 1860, he reorganized the Italian Army.

La Marmora served as premier of Piedmont from July 1859 to January 1860, as well as governor of Milan and the king's lieutenant in Naples. In September 1864 he again became premier, and as minister of foreign affairs in April 1866 he concluded Italy's alliance with Prussia against Austria. As chief of staff in the ensuing war, however, he was held responsible for the overwhelming defeat of the Italians by Austria at Custoza (June 24, 1866). La Marmora retired to private life shortly afterward, although, after Rome was annexed to the Kingdom of Italy in 1870, he was appointed the king's lieutenant there. Among his several works, Un po' più di luce sugli eventi politici e militari dell'anno 1866 (1873; “A Little More Light on the Political and Military Events of the Year 1866”) seeks to justify his actions at Custoza.