Marie was born in Karlsruhe. At the time of the war against France, she stayed at Prenzlau. In 1806, her father-in-law fled from the troops of Napoleon to Altona, where he died of the wounds he sustained in the war against France. Marie and her mother-in-law, Princess Augusta of Great Britain, came to see him at his sick-bed, but when the French army headed toward Hamburg, they were advised by the British ambassador to flee, and left shortly before his death. They were both invited to Sweden by Marie's brother-in-law king Gustav IV Adolf of Sweden. Augusta preferred to stay with her niece, Louise Augusta of Denmark in Augustenburg, but Marie accepted the offer and joined the king and queen of Sweden with her children at Malmö, were the royal family stayed without the royal court at the time to be close to the war during the difficult situation. Her spouse was granted permission by the emperor to stay in Altona. Her brother, the Hereditary Prince of Baden, was married to Stephanie de Beauharnais, and an ally of Napoleon, and joined the emperor in Berlin at the same time. Napoleon refused to see Marie's consort but said that he would like to see her, and Marie's brother wrote to her and asked her to come to Napoleon in Berlin as the ambassador of Brunswick to speak on behalf of her husband. She accepted the suggestion and travelled alone toward Berlin, but was stopped in Stralsundon the order of her husband, as it was believed at the time that Napoleon had plans to marry her to his brother Jérôme Bonaparte. Her husband was reportedly genuinely fond of her and visited her incognito in Sweden two times, despite the fact that Sweden was considered enemy territory by Napoleon. During her stay in Sweden Marie lived with the royal family in Malmö, where they stayed informally during her stay, rather than in state in Stockholm. She was reportedly used to an informal interaction with her ladies-in-waiting and felt restricted in the household of her strict and temperamental brother-in-law the king, whom she found it difficult to get along with. In May 1807, her sister, Queen Frederica, was leaving Malmö and returning to the court at Stockholm to give birth, and asked Marie to come with her, but her husband demanded her to return to Germany, which she did.
