1799, he
accepted employment from the Consulate, and from April 1800 till the
18th of August 1801 commanded the army in La Vendee. On the introduction
of the empire he was made one of the eighteen marshals of France, and,
from June 1804 to September 1805, acted as governor of the
recently-occupied Hanover. During the campaign of 1805, Bernadotte with
an army corps from Hanover co-operated in the great movement which
resulted in the shutting up of Mack in Ulm. He was rewarded for his
services at Austerlitz (December 2, 1805) by the principality of Ponte
Corvo (June 5, 1806), but during the campaign against Prussia, the same
year, was severely reproached by Napoleon for not participating with his
army corps in the battles of Jena and Auerstadt, though close at hand.
In 1808, as governor of the Hanse towns, he was to have directed the
expedition against Sweden, via the Danish islands, but the plan came to
nought because of the want of transports and the defection of the
Spanish contingent. In the war against Austria, Bernadotte led the Saxon
contingent at the battle of Wagram, on which occasion, on his own
initiative he issued an order of the day, attributing the victory
principally to the valour of his Saxons, which Napoleon at once
disavowed.

Bernadotte, considerably piqued, thereupon returned to Paris, where the
council of ministers entrusted him with the defence of the Netherlands
against the English. In 1810 he was about to enter upon his new post of
governor of Rome when he was, unexpectedly, elected successor to the
Swedish throne, partly because a large part of the Swedish army, in view
of future complications with Russia, were in favour of electing a
soldier, and partly because Bernadotte was very popular in Sweden, owing
to the kindness he had shown to the Swedish prisoners during the late
war with Denmark. The matter was decided by one of the Swedish couriers,
Baron Karl Otto Morner, who, entirely on his own initiative, offered the
succession to the Swedish crown to Bernadotte. Bernadotte communicated
Morner's offer to Napoleon, who treated the whole affair as an
absurdity. Bernadotte thereupon informed Morner that he would not refuse
the honour if he were duly elected. Although the Swedish government,
amazed at Morner's effrontery, at once placed him under arrest on his
return to Sweden, the candidature of Bernadotte gradually gained favour
there, and, on the 21st of August 1810, he was elected crown-prince.