He fought in André Masséna's Army of Switzerland, where he participated in the Winterthur and First and Second Battles of Zürich, the campaigns of 1806 against Prussia, and Napoleon's invasion of Russia.

[6] In the War of the Second Coalition, he participated in the French defeats at Ostrach and Stockach in March 1799, and served under the newly promoted Michel Ney on the forward line of defense of the Swiss city of Zürich.

At the Battle of Winterthur, he directed the rear guard action covering Ney's retreat through Winterthur, holding a key bridge cross of the Tōss River for 90 minutes against a larger Austrian force under command of Friedrich Freiherr von Hotze.

[7] A few days later, he was present for the defeat at the First Battle of Zürich when André Masséna withdrew the entire French force across the Limmat river.

He participated in French victories at Hohenlinden and later at Austerlitz, where he commanded the 2nd Dragoon Division[9] in Marshal Joachim Murat's Cavalry Reserve.

[11] At the Battle of Eylau in February 1807, he led his dragoons in Murat's famous 10,000-man cavalry charge depicted by Jean Antoine Siméon Fort, the 19th century history painter.

[12] At the Battle of Wagram (July 1809) Walther commanded four squadrons of Grenadiers à Cheval of Jean-Baptiste Bessières's Imperial Guard Cavalry.

[16] At the Second Battle of Kulm (17 September 1813), he commanded the Imperial Guard Cavalry including the dragoons, Grenadiers à Cheval, and 1st (Polish) and 2nd (Dutch) Lancers.

[18] After refitting and resupply at Erfurt, where Napoleon had stashed a large depot of arms and ammunition, the French army continued to withdraw through western Germany, toward the Rhine.