Charles Emmanuel was born in Turin, the eldest son of King Victor Amadeus III of Sardinia (at the time styled "Duke of Savoy") and of his wife Infanta Antonia of Spain. From his birth until his own succession to the throne of Sardinia in 1796 Charles Emmanuel was styled "Prince of Piedmont".
In 1775 Charles Emmanuel married Marie Clotilde of France, daughter of Louis, dauphin de France and Marie-Josèphe, and sister of King Louis XVI of France. Although the union was arranged for political reasons, Charles Emmanuel and his wife became devoted to each other. Their attempts to have children, however, were unsuccessful.
At the death of his father (October 14, 1796), Charles Emmanuel succeeded as King of Sardinia. The kingdom included not only the island of Sardinia, but also significant territories in north-west Italy including all of Piedmont.
At his succession to the throne in 1796, Sardinia was at war with the French Republic. By 1798 Charles Emmanuel had been forced to abdicate all his territories on the Italian mainland and to withdraw to the island of Sardinia. The following year he tried unsuccessfully to regain Piedmont. He and his wife lived in Rome and in Naples as guests of the wealthy Colonna family.
On March 7, 1802 Charles Emmanuel's wife Marie Clothilde died. He was so moved by her death that he decided to abdicate, June 4, 1802 in favour of his brother Victor Emmanuel. Charles Emmanuel retained the personal title of king. He lived in Rome and in the nearby town of Frascati.
In Frascati he was a frequent guest of his second-cousin Henry Benedict Stuart, Cardinal Duke of York, last member of the Royal House of Stuart. At Henry's death in 1807 Charles Emmanuel became the senior legitimate descendant of King Charles I of England and Scotland. Charles Emmanuel was therefore recognised by Jacobites as King Charles IV of England, Scotland, France and Ireland, although he himself made no public claim to the title.
In 1815 at the age of sixty-four Charles Emmanuel took simple vows in the Society of Jesus (the Jesuits). He was never ordained to the priesthood, but lived the rest of his life at the Jesuit novitiate in Rome.