He was part of the Brest division that left in late 1796 for the expedition to Ireland, where he served as artillery commander under General Jean Hardy.

[2] Appointed a member of the Légion d'honneur on 19 Frimaire of that year, then an officer of the order on 25 Prairial, Pernety was raised to the rank of brigadier general on 1st February 1805 and served in the Grande Armée during the campaigns of 1805 to 1807.

He was present at the battles of Ulm, Austerlitz and Jena, and directed the siege of Breslau with great talent and activity.

De Pernety took steps to ensure he was safe - though the explanation for this was met with a blank response from Gauss, who had never heard of a lady from Paris named Sophie Germain.

This leads me to confess that I am not as unknown to you as you may think, because, fearing the sense of ridicule associated with a female scientist, I previously preferred to adopt the name Monsieur Le Blanc to communicate to you those notes you had indulged me in reading..."[3] Awarded Commander of the Legion of Honour on 3 May and Major General on 11 July, he was awarded the Commander's Cross of the Military Order of Maximilian Joseph of Bavaria by the King of Bavaria.

In 1809 Pernety commanded the artillery of the 4th corps in the army of Germany under the orders of Marshal Masséna, and had the necessary boat bridges built across the Danube to capture the island of Lobau.

During the battle of Wagram, Marshal Masséna publicly praised General Pernety, who was created a Baron of the Empire and Grand Officer of the Legion of Honour on 21 July of the same year.

He had the honor of starting the Battle of Borodino and contributing to the capture of the Russian redoubts with skillfully directed fire.

In this capacity he rendered important services at the battles of Lützen and Bautzen, so much so that he received the Grand Cross of the Order of Reunion on May 3.