On 10 May 1796, the French army defeated the Austrian troops in the Battle of Lodi, and occupied the Duchy of Milan.

Napoleon set up a temporary authority, the General Administration of Lombardy, which replaced the Austrian administration and created a French client republic in Northern Italy, adopting the French Republican calendar.

The administration was granted full civil powers by a proclamation of Napoleon on Brumaire 8, year V (29 October 1796), although its orders had to be approved by the French military commander of Lombardy.

After the new victories of Napoleon's army, the territory of the republic grew; with the Peace of Leoben on 17 April 1797, France invaded the Republic of Venice, conquering Bergamo and moving eastwards from the Adda River to the Oglio River, the Venetian demarcation line established more than three centuries earlier.

On 19 May, Napoleon transferred to Milan the territories of the former Duchy of Modena from the bordering Cispadane Republic.