The name of the village appears for the first time in a document of the 937 as Garniano, perhaps derived from the Latin stem Garenius. Documents of Tito Livio and headstones, testify to the presence of Etruscans, Celts, Cenomani and Romans.
From 1350 to 1426 the territory of Gargnano was a dominion of the Visconti, later a dominion of the Republic of Venice.
Lorenzo Fiorini, Domenico Pattuccelli and Tommaso Chiaromonte, volunteers in the southern army of Giuseppe Garibaldi during the military campaign of 1860
Alexander Bettoni Cazzago, soldier, partisan and horseman. Won the Siena Square dressage competition in 1942. As colonel of the Third Regiment of the Savoy Cavalry in 1942 he led charges in the Russian campaign that are among the last uses of cavalry in modern warfare.