 After the wedding, De la Gardie was made a Privy Councillor.On 17 April 1648, he was promoted to general and served as such under the future king, and his own brother-in-law, Charles Gustav, during the conquest of Prague that took place in the final months of the Thirty Years' War.Despite making only a slight contribution in the war, De la Gardie was eventually rewarded 22,500 riksdaler, more than any other general.