His father Richard Garnett (1835-1906) was a writer and librarian at the British Museum. His wife was Constance Garnett, known for her translations of Russian literature, married on 31 August 1889; the writer David Garnett was their son, born 9 March 1892.
Garnett had only a few years formal education at the City of London School, leaving at the age of 16, but he educated himself further by reading widely. He gained a high reputation at the time for a mixture of good sense and sensitivity in relation to contemporary literature. His influence through his encouragement of leading authors exceeded by far that of his own writing. His literary contacts and correspondents spread far and wide, from Petr Kropotkin to Edward Thomas.
He worked as an editor and reader for the London publishing houses of T. Fisher Unwin, Gerald Duckworth and Company, and then Jonathan Cape. He brought together in 1898 Joseph Conrad, an Unwin author to whom he acted as a mentor as well as a friend, and Ford Madox Ford; they collaborated in the first few years of the twentieth century. Garnett befriended D. H. Lawrence, and for a time influenced him in the direction of realist fiction. He also had a role in getting T. E. Lawrence's work published. One of his failures was to turn down for Duckworth James Joyce's A Portrait of the Artist as a Young Man, in 1915. He was a strong supporter of John Galsworthy, and The Man of Property in the Forsyte Saga was dedicated to him. He also championed American writers Stephen Crane and Robert Frost and Australia's Henry Lawson, and helped the Irish writer Liam O'Flaherty.
His play The Breaking Point was not allowed a licence for dramatic performance in London under the censorship system of the time (Lord Chamberlain's office). Its publication was permitted, and in 1907 Garnett published the play, which dealt with an unmarried mother, together with an open letter to the censor. The letter was in fact written by the critic William Archer. This was one battle in a campaign being waged at the time, under the generalship of Bernard Shaw, to free the stage.
- An Imaged World (1894)
- The Art of Winnifred Matthews (1902)
- The Breaking Point, a Censured Play. With Preface and a Letter to the Censor (1907)
- Hogarth (1911)
- Tolstoy: His Life and Writings (1914)
- The great war in 1916, a neutral's indictment (1917) with Louis Raemaekers, H. Perry Robinson, and M. B. Huish
- Turgenev (1917) biography
- Papa's War and Other Satires (1918)
- Friday Nights; Literary Criticisms and Appreciations (1922)
- Letters from W. H. Hudson, 1901-1922 (1923) editor
- Letters from Joseph Conrad 1895-1924 (1928) editor
- The trial of Jeanne d' Arc and other plays (1931)
- Letters from John Galsworthy 1900-1932 (1934) editor
- Edward Thomas: A selection of letters to Edward Garnett (1981 reprint)
- Edward Garnett (1950) H. E. Bates
- The Garnett Family (1961) Carolyn G. Heilbrun,
- Edward Garnett; a life in literature (1982) George Jefferson