Alexander Tormasov came from an old noble family. At the age of ten years he started his services as Page of Honour, in 1772 he became a lieutenant of Vyatka infantry regiment but in few weeks went under command of Yakov Bruce as aide-de-camp. Three years later Tormasov has formed and headed the Finland chasseur regiment in the rank of lieutenant colonel. In 1782 Prince Potemkin charged to him an operation in Crimea. After that Tormasov received the Dolmatsky hussar regiment on the base of which and of Macedonian hussar regiment he formed and then commanded the Aleksandrian light cavalry regiment with the rank of colonel.
In 1788-1791 he took part in the Russo-Turkish War and was promoted to Major General on 21 March 1791. In 1792 and 1794 he successfully acted against the Polish-Lithuanian Commonwealth during the Polish-Russian War of 1792 and Kościuszko Uprising. Like many other generals of this time, he was dismissed by Emperor Paul I on 11 July 1799 and was imprisoned in the Dünamünde fortress for several months. On 16 November 1800 he was restored in the Army. On 15 September 1801, on the day of the coronation of Emperor Alexander I he was promoted to Full General of cavalry. Later he took up an administrative post until 1803.
From 1803 he served as governor of Kiev, Minsk and from 1807 Riga. From 1809 to 1811, he served as a Viceroy of Georgia and as the commander-in-chief in the Caucasus. After the French invasion of Russia began, on 25 March 1812 Alexander Tormasov became the Chief Commander of the Third Army of the West. After arrival of Pavel Chichagov he acted under command of Mikhail Kutuzov. After the death of Pyotr Bagration he commanded the Second Army of the West and later the Main Army. He was prominent in numerous battles, especially of Maloyaroslavets, Krasnoye and Lützen.
Because of poor health he left military service and became a member of the State Council. On 30 August 1814 he followed Count Fyodor Rostopchin as General Governor of the Moscow Governorate. Two years later he received a comital title.