Early career Buxhoeveden entered Russian military service in 1764 and took part in the
Russo-Turkish War (1768–1774). He married Natalia Alexeyeva in 1777, a connection that proved highly advantageous for his advancement at the Russian imperial court. He was promoted to colonel in 1783 and major general in 1789. His rapid rise owed more to his social connections than to his abilities as a commander. During the
Russo-Swedish War (1788–1790) he participated in the
first Battle of Svensksund in August 1789. In the
Polish–Russian wars of 1792–1794 he served as a divisional commander, and in 1795 was appointed military governor of the recently captured
Warsaw, where he actively worked to prevent violence against the city's population by Russian troops. He was granted a hereditary
countship by the King of
Prussia, a title subsequently also conferred on him in Russia. In 1797 he was appointed
Governor General of Saint Petersburg, but fell out of favour with
Tsar Paul I the following year and was exiled to his estates.
Napoleonic Wars In 1805, Buxhoevden commanded the left wing of the allied Russo-Austrian army at the
Battle of Austerlitz. The battle ended in defeat for the coalition forces. On , during the
War of the Fourth Coalition, Buxhoeveden was entrusted with a
corps of four
divisions. Tensions arose between him and
Bennigsen, and when Bennigsen's army fought the French at
Pultusk and
Golymin, Buxhoeveden remained inactive near
Maków Mazowiecki. He was subsequently relieved of command and replaced by Bennigsen.
Finnish War 1808–09 In 1808, Buxhoeveden was appointed commander-in-chief of the Russian forces invading
Swedish Finland and simultaneously placed in charge of the civil administration of the occupied territories. Former members of the
Anjala league – officers who had conspired against the Swedish king during the 1788–90 war – served on his staff and were tasked with the political incorporation of the territory, including issuing a proclamation promising to convene the Finnish Estates in
Turku. After besieging
Sveaborg, Buxhoeveden advanced with his main force to
Turku within a month, establishing his headquarters there. He devoted more attention to the administration of the occupied territory than to military operations. The occupation compared favourably with the earlier Russian occupation during the
Lesser Wrath of the 1740s: Buxhoeveden investigated incidents of violence by Russian troops and paid compensation from Russian imperial funds to those who had suffered harm. On 29 September he concluded the
Armistice of Lohtaja with the Swedish forces, a decision that caused considerable displeasure in Saint Petersburg, where he was considered to have exceeded his authority. He subsequently confirmed the
Convention of Olkijoki in November. Citing poor health, he relinquished command and was replaced as commander-in-chief by General
Bogdan von Knorring. == Estates ==