Stephens was a student of the Royal Academy of Arts, London and of William Holman Hunt. His attempts in painting dated between 1848-1850, but he destroyed most of his pictures. Only three of them are still at the Tate Gallery, London. He soon turned to art criticism, serving as art editor for the Athenaeum and being a contributor to the Art Journal and Portfolio. He wrote articles, monographs and catalogues on many artists, among them William Hogarth, Sir Joshua Reynolds, George Cruikshank, William Mulready, Thomas Bewick, Sir Lawrence Alma-Tadema, Thomas Gainsborough, Edwin Landseer, Samuel Palmer, Sir Anthony Van Dyck, William Holman Hunt, John Everett Millais, Thomas Woolner, Ford Madox Brown, and Edward Burne-Jones. In 1894, he published a Portfolio monograph on Dante Gabriel Rossetti. He died on March 9, 1907.
Stephens was also Keeper of the Prints and Drawings in the British Museum and wrote most entries in the first volumes of the Catalogue of Prints and Drawings in the British Museum, Division I: Political and Personal Satires.