[2] Carl Gustaf Tessin died at his country estate, Åkerö Manor, in 1770; he made numerous contributions to the development of Swedish culture throughout his life.

In 1725 Tessin was appointed ambassador at Vienna, and in that capacity counteracted the plans of the Swedish chancellor, Count Arvid Horn, for joining the anti-Russian Hanoverian Alliance.

[3] During the riksdags of 1726–27 and 1731, Tessin fiercely opposed the government, and his wit, eloquence, and imposing presence made him one of the foremost protagonists of the party subsequently known as "The Hats".

[3] On the division of the spoil of patronage he chose for himself the post of ambassador extraordinary at Paris, and from 1739 to 1742 delighted Versailles with his brilliant qualities of grand seigneur, at the same time renewing the traditional alliance between France and Sweden which had been interrupted for more than sixty years.

It was his sanguine credulity which committed the Hats to their rash and unconsidered war with Russia in 1741–42, though in fairness it must be added that Tessin helped them out of their difficulties again by his adroitness as party leader and his stirring eloquence.

It was a dignified and prudent policy, but his endeavour to consolidate it by promoting a matrimonial alliance between the two courts alienated the Swedish crown prince, who, as a Holsteiner, nourished an ineradicable hatred of everything Danish.

On the occasion of the coronation (1752) he resigned the premiership, and in 1754 the governorship of the young crown prince Gustavus also, spending the rest of his days at his estate at Åkerö Manor, where he died.

[5][6][7] Being heavily in debt on his return to Sweden, he was obliged to sell part of his collection to the then King Fredrik I, who gave them to Queen Louisa Ulrika.