Franz von Lauer entered the Imperial Army as a military engineer in 1755 and ended his career as Feldzeugmeister. After serving in the Seven Years' War, by 1783 he had reached the rank of oberst, or colonel. He fought against Ottoman Turkey at Belgrade and became a general officer for his distinguished effort as a siege specialist.

In the siege of Belgrade a Habsburg Austrian army led by Feldmarschall Ernst Gideon von Laudon besieged an Ottoman Turkish force under Osman Pasha in the fortress of Belgrade. After a three-week leaguer, the Austrians forced the surrender of the fortress. During the campaign which was part of the Austro-Turkish War, the Austrian army was greatly hampered by illness. Austria held the city until 1791 when it handed Belgrade back to the Ottomans according to the terms of the peace treaty. Several Austrian soldiers who distinguished themselves during the siege later held important commands in the subsequent French Revolutionary Wars and Napoleonic Wars. Belgrade is the capital of modern Serbia.