In 1777 he accompanied Emperor Joseph II (in the disguise of a "Count Falkenstein") on his visit to his sister Queen Marie Antoinette in France.

Immediately afterwards, Cobenzl travelled to Berlin as a Habsburg envoy, but was not able to prevent the Prussian king Frederic the Great from entering the War of the Bavarian Succession.

In 1779 he concluded the Peace of Teschen and assumed the office of an Austrian vice-chancellor, eventually succeeding State Chancellor Prince Wenzel Anton of Kaunitz-Rietberg in 1792.

However, already in March 1793 upon discords regarding the Second Partition of Poland, he had to resign from office in favour of Baron Johann Amadeus Francis de Paula von Thugut.

He was a patron of the arts, acquainted with Wolfgang Amadeus Mozart, and greatly contributed to the education and career of the Slovenian Neoclassicist painter Franz Caucig.