Noble. The eldest son of Alexander Gordon, 2nd Duke of Gordon, he was named because of his father's friendship with Cosmo III, the Grand Duke of Tuscany. Gordon studied law in the University of Leyden. He succeeded his father as 3rd Duke of Gordon in 1728. In 1741 he married Catherine, daughter of William Gordon, 2nd Earl of Aberdeen (1679 - 1746).
Gordon could not be persuaded by his younger brother, Lord Lewis, to join the Jacobite Rising of 1745. He was elected one of the Representative Peers of Scotland and was created a Knight of the Order of the Thistle.
In 1752, Gordon went on a tour through France, but died near Amiens aged only 32. His body was brought back from France to be laid in the chapel near Gordon Castle and finally interred in Elgin Cathedral.