Colloredo joined the Austrian "Carl Colloredo" Infantry Regiment Nr. 40 before the Seven Years' War as an ensign and distinguished himself at the Battle of Prague in 1757. He also fought at the Battle of Maxen in 1759 and at the Battle of Torgau in 1760 where the regiment withstood the first Prussian assault. For this exploit, Colloredo was promoted major. After fighting in several more actions, he was appointed lieutenant colonel of the "Waldeck" Infantry Regiment Nr. 35 on 1 April 1762. He replaced his brother Joseph as colonel of the "Lacy" Infantry Regiment Nr. 22 on 8 February 1764. He became a knight of the Teutonic Order in 1764. He earned promotion to major general on 1 May 1773 and to lieutenant field marshal on 10 April 1783.