In 1823 Clam-Gallas joined the Army, at first as a Rittmeister (Captain) of the 1st Cavalry Regiment in 1831, then Commander (1835), Colonel (1840) and General in Prague (1846).
In 1848, called to Italy under the orders of General Joseph Radetzky, he commanded a brigade which distinguished itself at Santa Lucia, Vicenza and the Battle of Custoza. He was decorated with the Military Order of Maria Theresa and promoted to Field Marshal Lieutenant (equivalent of two-star general).
In April 1849 he became commander of the Transylvanian Army Corps which needed to return to Turkey (7,000 infantry, 1,600 horse and 36 cannon). At the beginning of July he was moving into Hungary to Hungarian: Brassó (now Romanian: Braşov), to support Alexander von Lüders on the right flank. In this month there were a few battles between Lüders, Józef Bem and Sándor Gál. During the Transylvanian summer campaign, Clam-Gallas was defeated by Bem, but after that was able to defeat Sándor Gál and his Székels Army. After occupying Székely Land he joined Lüders and together they defeated Bem at Segesvár.
In 1850, he was head of the I Army Corps of Bohemia in Vienna, and in the Second Italian War of Independence (1859) took part in the Battle of Magenta and the Battle of Solferino. This army corps was one of the first to be repelled, but this failure had no personal consequences for Clam-Gallas, who was promoted to General der Kavallerie.
In 1861 he was admitted to the Aulic Council before becoming, in 1865, Imperial Hofmeister.
In the course of the Austro-Prussian War, he suffered a humiliating defeat at Jičín, for which he was court-martialled, but he was acquitted because of his position in society. He spent his final years in retirement in Frýdlant and Liberec in Bohemia (now the Czech Republic).