In Russia, he is viewed as a statesman who played a key role in establishing the Grand Duchy of Finland within the Russian Empire.

[1][3] The Royal Cadet School was closed down after four years because the monarch and the Riksdag of the Estates held differing political views.

[1][3] During the Pomeranian War, he served as an adjutant at the military headquarters of Count Axel von Fersen.

He was then transferred to an elite military group led by his younger brother, Jacob Magnus Sprengtporten.

Sprengtporten supported the Revolution of 1772 and took control of Viapori Fortress, persuading soldiers to join Gustav III's side.

He desired to join the American Revolutionary War to fight against the English rule, but due to French confusions, he was not dispatched to North America.

[3][1] Due in part to contacts with Benjamin Franklin who was there contemporaneously he conceived of the idea of separating the grand duchy from Sweden.

Sprengtporten's concept of a separate state was not original, as Empress of Russia Elizabeth proposed a new Kingdom of Finland in 1742.

[6][2] This aim was first approached through the Walhalla-orden subversive secret society and scheming with the king's brother, Charles XIII of Sweden.

Like his brother he also came to the conclusion that his services had not been adequately appreciated, and the flattering way in which he was welcomed by the Russian court during a visit to Saint Petersburg in 1786 still further incensed him against the perceived ingratitude of his own sovereign.

His own negotiations with his fellow countrymen, especially after Gustav III of Sweden had brought the treacherous army officers of the Anjala conspiracy back to their allegiance, failed utterly.

Emperor Paul sent him to negotiate with Napoleon concerning the Maltese Order and the interchange of Russian war prisoners in Holland in 1800.

[1] Sprengtporten presented Emperor Alexander I with a comprehensive plan in 1805 to establish the Kingdom of Poland and an independent Finland.

Instead, Sprengtporten served as an advisor to Count Friedrich Wilhelm Graf von Buxhoevden, who acted as the supreme commander.

[1] Sprengtporten lobbied the Russian Imperial Court vigorously, and Russia agreed to organise the Diet of Finland in Porvoo.

Sprengtporten never gained the friendship of Count Gustaf Mauritz Armfelt, who was the Chairman of the Committee for Finnish Affairs.

Sprengtporten resided on Vasilyevsky Island in Saint Petersburg during the winter and at his Hietala Estate near Vyborg, Grand Duchy of Finland, during the summer.

While staying in Teplice, Sprengtporten was in regular contact with the Count Waldstein's librarian, Giacomo Casanova.