secretary to Mary Stuart, Queen of Scots; he helped to arrange her marriage to Henry Stewart (Darnley, Henry Stewart, Lord), Lord Darnley.

Riccio was the son of a musician. In 1561 he went to Scotland with the Duke of Savoy's ambassador. After entering the Queen's service as a musician, he became (in December 1564) her French secretary, he being chosen for his trustworthiness rather than for his knowledge of the language. After her marriage, on July 29, 1565, he remained her close adviser and largely wrote her letters to the pope. Darnley's jealousy was exploited by Scottish nobles, who considered Riccio an arrogant parvenu and who desired his removal as the preliminary to the virtual deposition of Mary. Darnley seems to have harboured suspicions that Riccio was responsible for Mary's pregnancy.

While Darnley was present, the 4th Earl of Morton, Lord Ruthven, and other armed men dragged Riccio from Mary in her supper room in Holyroodhouse, Edinburgh, and stabbed him to death.