In 1813, he led a successful diplomatic effort to cause the Kingdom of Bavaria to change sides and join the Allies against Napoleon.

For notable service at the storming of Šabac in 1788, the emperor promoted the prince to Oberst (Colonel) of the Wenzel Colloredo Infantry Regiment # 56.

[2] In this action, Prince Johann of Liechtenstein and 2,000 cavalry crushed a force of 7,000 French troops, inflicting 2,000 casualties and capturing 2,000 more.

When the Austrian high command transferred Dagobert von Wurmser from Germany to Italy, Reuss and heavy reinforcements went with him.

During the first relief of the Siege of Mantua, the 45-year-old prince led a brigade in Peter Quasdanovich's column on the west side of Lake Garda.

[4] At first, operations went well for the Austrians, but Bonaparte defeated Quasdanovich in the complex Battle of Lonato and forced him to retreat to Riva del Garda.

At the height of the battle, on 3 August, Reuss seized Desenzano del Garda, rescuing some recently captured soldiers belonging to Joseph Ocskay's command.

His area of responsibility stretched from the northern tip of Lake Garda to Trento on the west side of the Adige river.

[6] On 3 September a 10,000-man French division led by Claude Belgrand de Vaubois drove his outposts out of Nago–Torbole on the lake.

During the Battle of Rivoli, the troops under Reuss bravely fought their way out of the river bottom to the plateau against tenacious resistance.

At this moment, a desperate French counterattack panicked some Austrians from the other columns and drove them to seek refuge in the river valley.

Disordered by fleeing troops and attacked from two sides by the French, Reuss' column retreated to the bottom of the gorge where their commander managed to rally them.

During the withdrawal from Italy that month, Reuss led a division in the left wing under Archduke Charles, retreating to Ljubljana (Laibach).

[14] The fog lifted around 11 am on 30 October and Reuss' troops were immediately assaulted by Guillaume Philibert Duhesme's division.

Caldiero village, held by his troops, changed hands several times during the day, as Duhesme attacked and Reuss counterattacked.

On 8 October, he signed the Treaty of Ried with Karl Philipp von Wrede, which resulted in the Kingdom of Bavaria switching sides and joining the allies against Napoleon.

He was Governor of the Duchy of Milan and Viceroy of Lombardy–Venetia in 1814–15, earning the Gold Medal for civilian service and the Order of the Iron Crown.