During the French Revolutionary Wars, he participated in an "outstandingly effective cavalry action" at Avesnes-le-Sec on 12 September 1793, where 4,663 Republican troops suffered losses of 2,000 killed and wounded with the Allies losing only 69 men. In addition, 2,000 soldiers and 20 artillery pieces were captured. He also participated in many other battles. Soon after being promoted to General-Major in June 1794, he fought at the Battle of Fleurus. He commanded a mixed cavalry-infantry brigade in Anton Sztaray's division at the Battle of Würzburg on 3 September 1796. After this action he was awarded the Commander's Cross of the Order of Maria Theresa. In the War of the Second Coalition, Liechtenstein commanded the Austrian Reserve at the Battle of Trebbia. In August 1799 he received promotion to Feldmarschal-Leutnant. He commanded 8,000 men in the successful siege of Cuneo in November and December. On 3 December 1800, he led a 5,109-man cavalry division in the Battle of Hohenlinden.
Liechtenstein was prominent in the Napoleonic Wars. At the Battle of Austerlitz, he led the 4,600 cavalry of the 5th Column. His troops fought well but he was unable to save the Austrian-Russian army from a disastrous defeat. Afterward, he carried on the negotiations with Emperor Napoleon I which concluded with the Peace of Pressburg. He earned the rank of General of Cavalry in 1808. Throughout the War of the Fifth Coalition Liechtenstein commanded the I Reserve Korps in the army of Archduke Charles. He led his cavalry and grenadiers at the Battle of Eckmühl on 22 April 1809, the Battle of Aspern-Essling on 21–22 May, and the Battle of Wagram on 5–6 July. He took command of the main army after Archduke Charles resigned and held this responsibility until the end of the year. Emperor Francis II promoted him Feldmarschallin September. He negotiated and signed the Peace of Schönbrunn. Both of these treaties were very favourable to Napoleon and hard on Austria. Afterward, Liechtenstein was accused of having little diplomatic skill. To escape criticism he resigned from the military in 1810.
Sovereign
As Prince of Liechtenstein, Johann made forward-thinking reforms, but also had an absolutist governing style. In 1818 he granted a constitution, although it was limited in its nature. He expanded agriculture and forestry and radically reorganized his administration, in an attempt to take the requirements of what was then a modern estate into account. He proved a trendsetter in the area of garden art by planting Biedermeier gardens and park landscapes in an English model. In 1806 Napoleon incorporated Liechtenstein in the Confederation of the Rhine and made it a sovereign state. At the Vienna Congress the sovereignty of Liechtenstein was approved. Liechtenstein became a member of the German Confederation in 1815. This membership confirmed Liechtenstein’s sovereignty. He was the 869th Knight of the Order of the Golden Fleece in Austria in 1806.
Princess Ida Leopoldine Sophia/e Maria/e Josepha/Josephine Franziska, Dame of the Imperial Court, Dame of the Order of the Starry Cross, married in Vienna on 30 July 1832 Karl/Carl 4te Fürst Paar Freiherr auf Hartberg und Krottenstein, Hereditary Grand-Master of the Posts of the Imperial Court, and had issue
Prince Rudolf Maria Franz Placidus, unmarried and without issue