In 1796, when the French with Napoleon Bonaparte entered Milan, he joined the National Guard of the Cisalpine Republic, as the second-in-command of Duke Gian Galeazzo Serbelloni.

On 15 October he was moved to the Lombard Legion as head of battalion and aide-de-camp to the Mantuan general Giuseppe Lahoz Ortiz, and in this capacity served during the French invasion of the Papal State.

At the Battle of Senio General Lahoz was wounded and he took command of the entire Legion, defeating the far more numerous Pontificians and capturing over one thousand prisoners, four banners and fourteen guns.

In December 1800 the nicknamed "Teulié Brigade" was attached to the division of General Brune, who was ordered to attack in the Tirol to cut the Austrian communication lines.

The short campaign was a complete success, and Brune later write on him: "We due every praise to the unshackable courage and capable direction of General Teulié".