Prince Charles saw her for the first time in Eutin in 1770 and remarked that she was pretty. The marriage was suggested in 1772, and the first ceremony took place in Wismar 21 June 1774: she arrived in Sweden 3 June. The wedding was celebrated very luxuriously; she arrived in Stockholm by gondola 7 June, and the wedding ceremony took place the same night, followed by a masquerade in Kungsträdgården. She was noted for her beauty — her waist measured a mere 48 cm (19") and her shoe size 31 (girls' size 13) — and, as the marriage of the monarch had not been consummated after nine years, there were hopes that she would provide an heir for the throne.
In January 1775, there were signs that she was pregnant. It was hoped that the question of succession was solved, and prayers were held in the churches. However, the signs soon proved to be false. The news of the false pregnancy also made the king decide to consummate his marriage and provide an heir to the throne personally.
She made a personal success with her cheerful temperament and became a centre of the royal court, where she was called "Little Duchess" and was noticed for her beauty and vividness, wittiness and ease with words. With these qualities she fulfilled a contemporary ideal, and she is more noted in history for her role in the court of Gustav III, than she is for her period as a Queen. In contrast to the shy queen, Sophia Magdalena of Denmark, "Duchess Lotta" was lively, witty and flirtatious and was in many ways the female center of the court.
She participated in the amateur theatre which were an important part at the royal court at the reign of Gustav III, both as an actress and as a dancer. Her dancing was seen as scandalous by some, as ballet dancers were during this age regarded as prostitutes. After having been subjected to criticism that she and Princess Sophia Albertina distracted the King from the affairs of state by pursuit of pleasure, she retired from the stage in 1783.
Her marriage was distant and both she and her spouse had extramarital affairs. Charles paid more attention to his lovers than to her; at the time of their marriage, he was in the middle of his relationship with Augusta von Fersen. Among her alleged lovers was Count Axel von Fersen, alleged lover of Marie Antoinette. Her intimate friendship with countess Sophie von Fersen inspired rumors of bisexuality which, true or not, were repeated throughout her time as royal Duchess, by both Francisco de Miranda in 1786 and later by Frederica of Baden. The rumours of her extramarital alleged affairs were given a lot of attention during her pregnancy in 1797.
She was indifferent to the affairs of her spouse as they gave her the opportunity to live more freely herself, and she expressed her frustration when her husband's lack of lovers made him more attentive toward her, which exposed her to his suspicions and accusations: "As long as he had his mistresses, things were better, but since the last one was exiled because she allowed herself to be insolent towards the King, and he has not provided himself with a new one, his temperament has gotten worse, and I have daily been subjected to outbursts because of this, which has occurred even in front of the staff. This hostility have increased so much during the winter that I have reached the end of my patience." She expressed her view upon love and sexuality when Gustav III refused to destroy documents of his late mother's alleged love affair with Count Gustav Tessin, and commented about the sexual double standards: "How sad it is to have a tender heart, for a tender nature is a misfortune as well as a blessing, and no one can resist the power of love (....) Yes, nothing is more true than the inscription upon the image of Eros: "Here is your true master, He is, He was, and He always will be." You must admit the misfortune of women: while men have their complete freedom, she is always burdened by prejudice and circumstance. (....) I am convinced that most women would ask for nothing more than to be transformed to men, so they could be freed from the unhappy bonds and enjoy complete freedom".
In 1782, she participated as a mediator in the reconciliation between Gustav III and his mother at her deathbed, after they had been in conflict since 1778, when the Queen Dowager supported the rumour that the Crown Prince was illegitimate and the son of Count Adolf Fredrik Munck af Fulkila.
In 1792, her spouse became regent during the minority of his nephew Gustav IV Adolf. The actual power was in the hands of his favorite, Count Gustaf Adolf Reuterholm, and she had no influence on the regency. In 1798-99, the spouses made a trip to Germany and Austria and visited Carlsbad, Berlin, Vienna and Hamburg.[8] In 1800, the ducal couple founded a theatre academy, Damatiska akademien, at court, but it was closed by the monarch.
In 1803, the Boheman affair caused a severe conflict between Gustav IV Adolf and the ducal couple. The mystic Karl Adolf Boheman (1764–1831) had been introduced to them by Count Magnus Stenbock in 1793 and gained great influence by promising to reveal scientific secrets about the occult. Boheman inducted them to a secret society and founded what he described as a branch of the Freemasons in 1801, where both sexes were accepted as members, and to which the Counts and Countesses Ruuth and Brahe as well as the mother of the queen were introduced. Boheman was arrested upon an attempt to recruit the monarch, who accused him of revolutionary agendas and expelled him. The ducal couple were exposed to an informal investigation by the monarch, and the duchess was questioned in the presence of the royal council.
In 1809, the ducal couple was placed on the throne after the aristocratic coup deposing the monarch. During the coup, she stated: "I do not wish to be a Queen!",and she was later to say that she found it embarrassing to take the place of another.
When her spouse was informed he was King, she told him that she would become his reliable adviser and confidante, but keep away from the matters of the state. During his reign, she is known to have visited him in his bedroom every morning to talk to him.She was crowned with the king 29 June 1809. At the coronation, she was described as gracious and dignified without losing her usual vividness and cheerfulness.
Queen Hedvig Elizabeth Charlotte held a salon, the so called "Green table", where women discussed politics while sewing. After a performance of the blind musician Charlotta Seuerling, she gave her protection to the university for the blind and deaf, which was founded by Per Aron Borg and the first of its kind in Sweden. She also restored the Royal Swedish Opera.
Before the arrival of Augustenburg, the King suffered a stroke and became unable to reign, whereupon she informally presided over the council in his place. The Gustavian party asked her to accept the post of regent, exclude the newly appointed Augustenburg and adopt the former Crown Prince Gustav as heir.
She declined the offer to be regent, and the coup never took place.
The election of a new heir to the throne was held in Örebro.
When Jean Baptiste Bernadotte was elected, the government sent her Fredrik August Adelswärd as their representative to inform her. He said that realized her disappointment, as Bernadotte was a non-royal, but asked her to pretend to be happy for the health of the monarch, who was afraid that she would displeased. She answered that she would be happy with any one who could bring stability.
Bernadotte ordered the removal of everything reminding of the deposed royal family. Her Gustavian views made the anti-Gustavians direct the suspicions of Bernadotte to her, and she was obliged to stop her correspondence with former Queen Frederica (1813), but her relationship with Bernadotte remained good. She supported his plan to conquer Norway, and became Queen of Norway in 1814. In 1816–1817, governor Baron Olof Rudolf Cederström attempted to implicate her in an alleged poison attempt against the life of the Crown Prince and his son. She had him questioned for slander, but this led to a break in the relationship with the Crown Prince, though it deepened her relation to Prince Oscar, who took her side in the affair.
At the death of her spouse, she said that she would not be able to survive him. After the funeral, a great conflict of some sort is reported to have taken place between the Queen Dowager and the King. After a private dinner with the King, she withdraw to her room to write, and the same night, she fainted and died.