Struensee became town physician of Altona (then in Denmark, now in Germany) in the 1760s. Through acquaintance with certain Danish courtiers, he was named to accompany the mentally unstable Christian VII on a European tour (1768–69), a post that led to Struensee's appointment as court physician in 1769. Dominating the king, he became the lover of Queen Caroline Matilda in 1770. He was soon able to abolish the council of state and the office of statholder (governor) of Norway in 1770. In June 1771 he had the king name him privy Cabinet minister, and in July he was made a count.

From March 1771 until January 1772 Struensee introduced a number of reforms, including freedom of the press, reduction of peasant labour service, a unitary judiciary, and reform of Copenhagen's municipal government. Having alienated many officials, however, he was the victim of a conspiracy in January 1772, when he was arrested and tortured to death for his liaison with the queen.