commander of the naval forces of Tuscany and then of Naples (Naples, Kingdom of) who as prime minister of Naples allied that kingdom with England and Austria in the period of the French (French revolutionary and Napoleonic wars) Revolution.

Finding the French Navy unappreciative of his skills, Acton, the son of an expatriate Englishman, joined the forces of Peter Leopold (later Holy Roman emperor Leopold II), grand duke of Tuscany, and distinguished himself by commanding a Tuscan squadron when Spain and Tuscany joined forces against Algeria (1774). In 1779 Peter Leopold's brother-in-law Ferdinand IV (Ferdinand I) of Naples invited Acton to reorganize the Neapolitan fleet, of which Acton soon became commander.

A favourite of Ferdinand's wife, Maria Carolina, he rose rapidly, disposing of all rivals, becoming minister of the navy, of war, of finance, and finally prime minister with almost absolute powers. His English and Austrian alliances weakened the traditional ruling class and the clergy, which had close ties with Spain. In addition, he engaged Naples in a long struggle against the French Revolution, the liberal ideals of which he opposed.

When the French attacked Naples in 1798, Acton fled to Sicily with the King and Queen aboard the ship of Horatio Nelson (Nelson, Horatio Nelson, Viscount), the British admiral. Naples was declared the Parthenopean Republic, but when Ferdinand regained control of Naples five months later, he instituted a reign of terror against those who had supported the French, for which Acton and Nelson must bear principal responsibility.

Acton stayed in power with only one brief interruption until the French attacked Naples again in 1806, and then he fled to Sicily with the royal family. He was the grandfather of the 1st Baron Acton, the renowned 19th-century historian.