Born 19 June 1783, Horncastle, Lincolnshire, England. 1792, emigrated with actor parents to Charleston, S.C. Studied art with schoolmate Charles Fraser; brother-in-law, Jean Belzons; and brother, Lawrence Sully, all miniature painters. He, too, began as a miniaturist. Until his brother's death in 1803, they painted together.
1805, married widowed sister-in-law. 1806, moved to New York. Patronage from acquaintances in theater. 1807, brief study with Gilbert Stuart, Boston. 1808, moved permanently to Philadelphia, where he soon became a leading portraitist. 1809, with funds from Philadelphia patrons, spent nine months in London studying under Thomas Lawrence. 1812, elected academician, Pennsylvania Academy of the Fine Arts.
After death of Charles Willson Peale, 1827, he was pre-eminent portrait painter of Philadelphia for remainder of life. 1837–38, London to paint portrait of Queen Victoria; major success. 1843, declined presidency of Pennsylvania Academy. Traveled frequently to other cities to execute portraits. His register of commissions lists over 2,600 paintings. Died 5 November 1872, Philadelphia.
William Kloss Treasures from the National Museum of American Art (Washington, D.C. and London: National Museum of American Art with the Smithsonian Institution Press, 1985