Starting his career of public service at 26 running the Venetian Arsenal and dockyard, Carlo Ruzzini became a diplomat and was sent as Ambassador to Madrid in 1691.

As the ambassador to Vienna, in July 1698 he was organizing the visit of the Russian Tsar Peter the Great to Venice, but that tour was failed because of the Streltsy revolt in Moscow.

This episode however did not stunt his career, as is demonstrated later by his appointment first as Venetian Ambassador in The Hague (1706), to the Turkish Court (1707) and in Vienna.

At the conclusion of the last of the wars between Venice and Turkey (1714–1718), Ruzzini represented the Republic during the peace negotiations at Passarowitz in July 1718.

After the Treaty of Passarowitz Ruzzini continued his diplomatic career with a second posting to Constantinople before ill health forced him home.