Johann Friedrich entered the University of Halle on August 5, 1752 at the age of fifteen where he studied medicine, and graduated on December 12, 1757. The university exposed him to Age of Enlightenment ideals, and social and political critique and reform. He supported these new ideas, becoming a propagandist for atheism, the writings of Jean-Jacques Rousseau, and the Encyclopédie.
When Adam and Maria Dorothea Struensee moved to Altona in 1758, where the elder Struensee became pastor of Marienkirche (Mary’s Church), Johann Friedrich moved with them. He was soon employed as a public doctor in Altona, in the estate of Count Rantzau, and in the Pinneberg District. His wages were meager, and he expected to supplement them with private practice.
His parents moved to Rendsburg in 1760 where Adam Struensee became first superintendent (comparable to bishop) for the duchy, and subsequently superintendent-general of Schleswig-Holstein. Johann Struensee, now 23 years old, had to set up his own household for the first time. His lifestyle expectations were not matched by his economics. His superior intelligence and elegant manners, however, soon made him fashionable in the better circles, and he entertained and scandalized his contemporaries by his controversial opinions and his frank licentiousness.
He was ambitious, and petitioned the Danish government in the person of Denmark’s Minister of Foreign Affairs Johann Hartwig Ernst, Count von Bernstorff for funds. He tried his hand at writing Enlightenment treatises. He saw himself as having a higher calling than a simple doctor.
June-July 1767 the king had spent the summer in Schleswig-Holstein, along with his court and chancellery. Struensee was a clever doctor, and having somewhat restored the king's health while visiting the area, gained the king's affection. He was retained as travelling physician on April 5, 1768, and accompanied the entourage on the King’s foreign tour to Paris and London via Hannover from May 6, 1768 to January 12, 1769. He was given the title of State Councilor (‘’etatsråd’’) on May 12, 1768, barely a week after leaving Altona.
During the nine month trip he developed a close relationship with the king. The king’s ministers Bernstorff and Finance Minister H.C. Schimmelmann saw Struensee as having a positive influence on the king, and stood behind his being named the king's personal physician January 1769 after their return to Copenhagen.
On September 15 the King dismissed Bernstorff, and two days later Struensee becomes maître des requêtes (privy counsellor), consolidating his power and starting the 16 month period generally referred to as the "Time of Struensee". On December 8 the king dismisses his entire state council and chancellery.
When in the course of the year the king sank into a condition of mental torpor, Struensee's authority became paramount.
Next, he dismissed all department heads, and abolished the Norwegian stadholderships. Henceforth the cabinet, with himself as its motive power, became the one supreme authority in the state. Other reforms included the establishment of foundling hospitals, the abolition of capital punishment for theft and of the employment of torture in judicial process, the doing away with such demoralizing abuses as perquisites, and of "lackeyism," or the appointment of great men's domestics to lucrative public posts.
Struensee held absolute sway for ten months, between March 20, 1771 and January 16, 1772. During this time he issued no fewer than 1069 cabinet orders, or more than three a day. For this reason, he has been criticized for having an imprudent "mania" for reform.
Other criticisms of Struensee are that he did not respect native Danish and Norwegian customs, seeing them as prejudices and wanting to eliminate them in favor of abstract principles. He also did not speak Danish, conducting his business in German. In order to be sure of obedience he dismissed wholesale without pension or compensation the staffs of all the public departments, substituting for old and experienced officials nominees of his own, in many cases untried men who knew little or nothing of the country they were supposed to govern.
While initially the Danish people favored his reforms, they began to turn against him. When Struensee abolished all censorship of the press, it only resulted in a flood of anti-Struensee pamphlets.
Still in spite of all his blunders, it is clear that, for a short time at least, middle-class opinion was, on the whole, favourable to him; and had he been wise, he might perhaps have been able to defy any hostile combination. What incensed the people most against him was the way in which he put the king completely on one side; and this feeling was all the stronger as, outside a very narrow court circle, nobody seems to have believed that Christian VII was really mad, but only that his Will had been weakened by habitual ill usage; and this opinion was confirmed by the publication of the cabinet order of July 14, 1771, appointing Struensee "gehejme kabinetsminister", with authority to issue cabinet orders which were to have the force of royal ordinances, even if unprovided with the royal sign-manual.
Nor were Struensee's relations with the queen less offensive to a nation which had a traditional veneration for the royal House of Oldenburg, while Caroline Matilda's shameless conduct in public brought the Crown into contempt. The society which daily gathered round the king and queen excited the derision of the foreign ambassadors. The unhappy king was little more than the butt of his environment, and once, when he threatened his keeper, Brandt, with a flogging for some impertinence, Brandt, encouraged by Struensee and the queen, actually locked him in his room and beat him with his fists until he begged for mercy.
Things were at their worst during the winter of 1771. Struensee, who had, in the meantime, created himself a count, now gave full rein to his licentiousness and brutality. If, as we are assured, he publicly snubbed the queen, we may readily imagine how he treated common folk. Before long the people had an opportunity of expressing their disgust openly.
The king, queen, Struensee and Enevold Brandt, along with the royal court spent the summer of 1771 at Hirschholm Palace north of Copenhagen, and stayed there until late in the autumn. On July 7 the Queen gave birth to a daughter, Louise Augusta; and a proclamation commanded that a Te Deum in honour of the event should be sung in all the churches. But so universal was the belief that the child was Struensee's that, at the end of the ordinary services, the congregation rose and departed en masse.
The general ill will against Struensee, which had been smouldering all through the autumn of 1771, found expression at last in a secret conspiracy against him, headed by Rantzau-Ascheburg and others, in the name of the Queen Dowager Juliana Maria, who in this way wrested power away from the king, and secured her and her son’s position of power for many years to come.
Early in the morning of January 17, 1772, Struensee, Brandt and Queen Caroline Matilda were arrested in their respective bedrooms, and the perceived liberation of the king, who was driven round Copenhagen by his deliverers in a gold carriage, was received with universal rejoicing. The chief charge against Struensee was that he had usurped the royal authority in contravention of the Royal Law (Kongelov). He defended himself with considerable ability and, at first, confident that the prosecution would not dare to lay hands on the queen, he denied that their liaison had ever been criminal. But on hearing that she was also a prisoner of state at Kronborg Castle, his courage evaporated, and he was base enough to betray her, though she did all in her power to shield him.
On April 28 Struensee and Brandt were condemned first to lose their right hands and then to be beheaded; their bodies were afterwards to be drawn and quartered. Sentence of death was the least that Struensee had to expect. He had undoubtedly been guilty of lèse majesté and gross usurpation of the royal authority, both capital offences according to paragraphs 2 and 26 of the Kongelov. He awaited his execution at Kastellet. The sentences were carried out on the April 28, 1772 with Brandt suffering first.
His affair with the queen was intolerable to the public at large, although sexual infidelity was not unusual in royal circles, and the king himself was notorious for his sexual exploits. Judgement of the queen's affair was much harsher than that accorded the king, and Victorian-era morality in the next century was not kinder to either Struensee or Caroline Matilda.
The King himself considered Struensee a great man, even after his death. Written in German on a drawing the king made in 1775, three years after Struensee’s execution, was the following: "Ich hätte gern beide gerettet" ("I would have liked to have saved them both"), referring to Struensee and Brandt.