Leopold Freiherr von Hauer was born on the 26th of January 1854 in Budapest. His father Stephan, who was a chief of section at the Ministry of the Interior was married to Antonia Gräfin Welsersheimb. The family who also had branches in Bavaria and Austria had entered the Bavarian nobility with the rank of "Freiherr" in 1792, the Austrian in 1793 and Leopold's grandfather Joseph, the Hungarian nobility on account of his military career. Some of his ancestors had distinguished themselves during the 2nd Ottoman Siege of Vienna (1683) and the War of the Spanish Succession (1701-1714). Leopold followed the military tradition of his family and entered at the age of 10 the cadet institute at Marburg. Passing through the Theresian Military Academy with "excellent success" he was commissioned as a Leutnant in hussar regiment number 11 on the 30th of August 1872. After attending the brigade officers' school in 1874/75 he was attached to the household of Erzherzogin Elisabeth where he became the tutor of young Erzherzog Eugen. In 1879 he was transferred back to his regiment, meanwhile promoted to Oberleutnant on the 1st of May 1877. In 1883 he attended the Militär-Reitlehrer-Institut (riding instructor's institute) and received his promotion to Rittmeister 2nd class on the 1st of May 1885. On the 1st of January 1889 he was promoted to Rittmeister 1st class shortly followed by the award of the Prussian Order of the Crown 3rd class. In 1892 he was again appointed to the court and was transferred to the household of Erzherzogin Stephanie, the widow of the heir to the throne Erzherzog Rudolf, as Dienstkämmerer (Duty Chamberlain). During this more than three years of court duty he received his promotion to Major on the 1st of November 1894. In 1895 he was transferred back to the troops but now to hussar regiment number 5 receiving for his performance with the household the commendation of the Kaiser, which allowed him to wear the bronze military merit medal (Signum Laudis) on the 21st of May 1895. On the 27th of August 1896 he assumed command of the cavalry cadet institute at Mährisch-Weißkirchen, where he received his promotion to Oberstleutnant on the 1st of May 1897. For his achievements in the education of cavalry cadets he was honored with the award of the Military Merit Cross on the 2nd of December 1898. Additionally he received the following foreign awards: the commander's cross of the Wasa-Order of Sweden, the Honorary Commander's cross of the House and Merit order of Oldenburg and the 2nd class of the Persian Order of the Sun and the Lion.
In March 1900 he assumed command of hussar regiment number 16 shortly followed by his promotion to Oberst on the 1st of May 1900. During the same year he married Elisabeth Fiano, a widow (born as Scheichenberger) who brought a daughter, Antonia to the union. As this marriage remained childless they adopted in 1914 the husband of Antonia, a son of General Conrad von Hötzendorf who then took the name Arnold Freiherr Conrad-Hauer. Leopold Freiherr von Hauer stayed as a regimental commander during the next 6 years receiving the Order of the Iron Crown 3rd class on the 16th of April 1904. In October 1906 the took over command of the 13th cavalry brigade followed by his promotion to Generalmajor on the 1st of November 1906. In July 1907 he switched to the command of the 4th calvalry brigade where he received the commanders' cross 1st class of the Order of Albrecht the Bear of the Duchy of Anhalt. He distinguished himself during the manouvres in 1910 and received excellent evaluations from his commanding officer General Freiherr von Kirchbach who highly recommended him for promotion and a more senior command. On the 1st of November 1910 he received his promotion to Feldmarschall-Leutnant and was appointed to the important post of Honvéd-Kavallerie-Inspector in December of the same year. During the following years he tried to increase the education level of the cavalry officers in the Hungarian territorial forces. For his efforts he was honored with the award of the knights' cross of the Order of Leopold on the 24th of September 1912 and the following foreign orders: the grand cross of the Military Merit Order of Spain (1910), the grand cross of the Military Merit Order of Bulgaria (1910) and the 2nd grade of the 2nd class of the Chinese Order of the Double Dragon (1911).
When the war started in August 1914 he assumed command of the 9th cavalry division which was part of the 1st army. Hauer and his division was mainly responsible for reconnaissance and took part in the battle of Krasnik. During the battle of Komarów he was engaged as cover for the Army group of Erzherzog Peter Ferdinand. Between October 1914 and May 1915 Hauer's division was enlarged, by attaching the 2nd cavalry division and temporarily also the 7th cavalry division and the German 8th cavalry division, to the "Kavalleriekorps Hauer". On the 1st of November 1914 Leopold Freiherr von Hauer was promoted to General der Kavallerie mit Titel und Charakter. (Brevet General of Cavalry). In November 1914 he was on the left wing of the 1st army of General Dankl and was then transferred to the Korps Tersztyánszky with the 2nd army further taking part in the battle of Limanowa-Lapanów. During the winter 1914/15 Hauer's corps was put under the command of the German Korps Gallwitz. For his outstanding performance he was honored with the award of the 2nd class of the Order of the Iron Crown with war decoration on the 2nd of December 1914 and the 2nd class of the Military Merit Cross with war decoration on the 8th of February 1915. For both decorations he later received the newly introduced swords. Meanwhile substantively promoted to General der Kavallerie (1st February 1915) he also received the Prussian Iron Cross 1st and 2nd class. During the May offensive in 1915 the Kavalleriekorps Hauer crossed the Vistula and later, now attached to the German Army group Frommel, reached Rosbach north of the Bialowieza forest. In September 1915 the corps was disbanded and Hauer's 9th cavalry division was transferred to Kowel where a new Kavalleriekorps Hauer was raised in October. Attached to the command of the German General von Linsingen they had to cover the roads between the rivers Styr and Stochod. After the front stabilized they had a relatively quiet winter and spring.
Not until July 1916 did Hauer's troops become involved in the aftermath of the Brussilow-offensive. After heavy fighting along the Stochod, followed by the defeat of the brigade of the Polish Legion which was attached to Hauer, there was continuing heavy fighting in the vicinity of Tobol in August and September 1916. During the autumn it was again possible to stabilize the front. During 1916 Freiherr von Hauer was honored with the title of Geheimer Rat (Privy Councillor) on the 16th of March 1916 and received the 1st class of the decoration of the Society of the Red Cross with war decoration (2nd August 1916), the grand cross of the Order of the Iron Crown with war decoration (13th September 1916) and the grand cross of the Bavarian Military Merit Order with swords. After another relatively quiet winter the Kavalleriekorps Hauer was able to capture the Russian bridgehead at Tobol during a surprise attack at the end of March and beginning of April 1917. For this unexpected victory he was honored with the 1st class of the Order of Leopold with war decoration and swords on the 17th of April 1917. On the 1st of August 1917 Freiherr von Hauer received his promotion to Generaloberst with seniority from the 12th of August 1917.
Following the revolution in Russia the war on the eastern front became quiescent . In October 1917 the Kavalleriekorps Hauer was disbanded. Some of his troops went to the Tyrol as formed units while others were completely broken up and distributed to other units. Generaloberst Hauer was sent on a leave awaiting a new command but there was no further use for a cavalry commander in his rank. In June 1918 he retired to Budapest. After the collapse of the Dual Monarchy he decided to became an Hungarian citizen. In November 1921 he was remarried to Karoline Kubinyi von Felsö-Kubin, his first wife having died in 1911. The couple lived in Budapest until Generaloberst Leopold Freiherr von Hauer died on the 3rd of May 1933.