To the second number of the "Cornhill Magazine" he contributed "An Essay without End," and this led to an introduction to Thackeray. In 1862, when Thackeray resigned the editorship of the "Cornhill", Greenwood became joint editor with G. H. Lewes. In 1864 he was appointed sole editor, a post which he held until 1868. While at the "Cornhill" he wrote an article in which he suggested, to some extent, how Thackeray might have intended to conclude his unfinished work "Denis Duval". In its pages appeared the "sensation" novel "Margaret Denzil's History", Greenwood's most ambitious work of fiction, also published in volume form in 1864.