structural:scholar_edition, quality:correction
Offer of the Swedish throne

In 1810, Bernadotte was about to enter his new post as governor of Rome when he was unexpectedly elected the heir-presumptive to King Charles XIII of Sweden. The problem of Charles's successor had been acute almost from the time he had ascended the throne a year earlier. He was 61 years old and in poor health. He was also childless; Queen Charlotte had given birth to two children who had died in infancy, and there was no prospect of her bearing another child. Soon after his coronation, the king had adopted a Danish prince, Charles August, who had died just a few months after his arrival. Despite the fact that Napoleon favored his ally Danish King Frederick VI, Danish Prince Frederick Christian initially had the most support to become the Swedish Crown Prince.

The political situation internally and externally for Sweden meant that selecting a foreign king was an attractive option. Sweden wanted to strengthen its relationship with Napoleon for militaristic reasons and so sought to select a king who would be able to attract Napoleon's support. The Swedish court initially sounded out the emperor for his preferences on candidates for crown prince, whereupon Napoleon made it clear he preferred his adopted stepson Eugène de Beauharnais, or one of his nephews or brothers. The Swedish envoys did not accept Eugène as a candidate. Baron Lagerbielke, the Swedish envoy in Paris, reported to Stockholm that Eugène was "gentle and good," "but he does not seem to be a man of strong character; and, although he had had great opportunities, he does not appear to have developed any distinguishing talents." Also, Eugène, serving as viceroy in Italy, did not wish to convert to Lutheranism, a prerequisite for accepting the Swedish offer. Moreover, none of Napoleon's brothers were interested in going to Sweden and his nephews were too young, as the Swedes did not want the hazards of minority rule in the event King Charles died prematurely. The matter was decided by an obscure Swedish courtier, Baron Karl Otto Mörner (nephew of Count Gustav Mörner, the commander of the Swedish force captured by Bernadotte at Lübeck), who, entirely on his own initiative, offered the succession to the Swedish crown to Bernadotte. Bernadotte communicated Mörner's offer to Napoleon who at first treated the situation as an absurdity, but later came around to the idea and while adopting a public attitude of indifference, quietly lent support to Bernadotte's candidacy both financially and diplomatically.

Although the Swedish government, amazed at Mörner's effrontery, at once placed him under arrest on his return to Sweden, the candidature of Bernadotte gradually gained favour and on 21 August 1810 he was elected by the Riksdag of the Estates in Örebro to be the new crown prince, and was subsequently made Generalissimus of the Swedish Armed Forces by the King. Several factors benefitted Bernadotte's election. Being foreign was, although problematic, also to his favour due to geopolitical factors and the internal situation at the time. One benefit was his (presumed) close ties to French Emperor Napoleon Bonaparte, with whom a relationship would provide military backing as the intention at the time was to reacquire Finland. The current King, Charles XIII, viewed Napoleon in a more positive way than Gustav IV Adolf had, who had held him in very ill regard. Another point in favour was that a large part of the Swedish Army, anticipating conflict with Russia, were in favour of electing a soldier. Also, Bernadotte was personally popular, owing to the kindness he had shown to the Swedish prisoners in Lübeck and his reputation as the well-liked governor of the Hanseatic Cities from 1807 to 1809; as many Swedish merchants had operated under his auspices. Finally, Bernadotte had no qualms about converting to Lutheranism, recalling the conversion of Henry IV for the benefit of France with whom he felt a kinship as both hailed from Pau, nor converting his son Oscar (though his wife Désirée never did renounce Catholicism).

Before freeing Bernadotte from his allegiance to France, Napoleon asked him to agree never to take up arms against France. Bernadotte refused to make any such agreement, upon the ground that his obligations to Sweden would not allow it; Napoleon exclaimed "Go, and let our destinies be accomplished" and signed the act of emancipation unconditionally. Many were also optimistic that Sweden would recover Finland under Charles John. The Swedish crown prince even unsuccessfully sought Napoleon's support to assist Sweden in conquering Norway.