(William) Denis Johnston (18 June 1901 – 8 August 1984) was an Irish writer. Born in Dublin, he wrote mostly plays, but also works of literary criticism, a book-length biographical essay of Jonathan Swift, a memoir and an eccentric work on cosmology and philosophy. He also worked as a war correspondent, and as both a radio and television producer for the BBC. His first play, The Old Lady Says "No!", helped establish the worldwide reputation of the Dublin Gate Theatre; his second, The Moon in the Yellow River, has been performed around the globe in numerous productions featuring such actors as Jack Hawkins, Claude Rains and Errol Flynn, although not all in the same production. He played a role in the 1935 film version of John Millington Synge's Riders to the Sea.
Johnston was a protégé of WB Yeats and Shaw, and had a stormy friendship with Seán O'Casey. He was a pioneer of television and war reporting. He worked as a lawyer in the 1920s and 1930s before joining the BBC as a writer and producer, first in radio and then in the fledgling television service.
During the Second World War he served as a BBC war correspondent, reporting from El Alamein to Buchenwald. For this he was awarded an OBE, a Mentioned in Despatches and the Yugoslav Partisans Medal. He then became Director of Programmes for the television service.
Johnston later moved to the United States and taught at Mount Holyoke College, Smith College and other universities. He kept extensive diaries throughout his life, now deposited in the Library of Trinity College, Dublin, and these together with his many articles and essays give a distinctive picture of his times and the people he knew. He received honorary degrees from the University of Ulster and Mount Holyoke College and was a member of Aosdána.
The Denis Johnston Playwriting Prize is awarded annually by Smith College Department of Theatre for the best play, screen play or musical written by an undergraduate at Smith, Mount Holyoke, Amherst and Hampshire Colleges and the University of Massachusetts Amherst.
Hilton Edwards, who first directed The Old Lady Says "No!", said that the script "read like a railway guide and played like Tristan and Isolde."  Brooks Atkinson in the New York Times, reviewing The Moon in the Yellow River, said "Mr Johnston does not explain; he irradiates."  Johnston's war memoir Nine Rivers from Jordan reached the New York Times Bestseller List and was cited in the World Book Encyclopedia's 1950s article on World War II under "Books to Read", along with Churchill, Eisenhower et al. Joseph Ronsley cites an unnamed former CBS Viet Nam correspondent who called the book the "Bible", carrying it with him constantly, "reading it over and over in the field during his tour of duty."
Johnston's apostrophe to Dublin, "Strumpet city in the sunset," from the closing speech of The Old Lady says "No!", has achieved its own fame. James Plunkett titled his epic novel of Dublin before the First World War Strumpet City. And a travel guide written by Harvard students in introducing Dublin made a classic misattribution: "James Joyce loved his 'Strumpet city in the sunset'." 
- The Old Lady Says "No!" (1929)
- The Moon in the Yellow River (1931)
- A Bride for the Unicorn (1933)
- Storm Song (1934)
- Blind Man's Buff (1936) (with Ernst Toller)
- The Golden Cuckoo (1939)
- King of Spain's daughter (1939)
- In Search of Valour (1939)
- The Dreaming Dust (1940)
- A Fourth for Bridge (1948)
- 'Strange Occurrence on Ireland's Eye' (1956)
- Tain Bo Cuailgne – Pageant of Cuchulainn (1956)
- The Scythe and the Sunset (1958)
- In Search of Swift (1959)
- John Millington Synge (1965)
- Nine Rivers from Jordan (1953)
- Orders and Desecrations (1992) (ed. Rory Johnston)
- The Brazen Horn (1976)
- Adams, Bernard. Denis Johnston: A Life. Lilliput Press, 2001.
- Barnett, Gene A. Denis Johnston. Twayne's English Authors Series No. 230. G.K. Hall & Co., 1978.
- Ferrar, Harold. Denis Johnston's Irish Theatre. Dolmen Press, 1973.
- Igoe, Vivien. A Literary Guide to Dublin. Methuen, 1994.
- Ronsley, Joseph, ed., Denis Johnston: a retrospective. Irish Literary Studies No. 8, Colin Smythe, Barnes & Noble Books, 1981.
- Denis Johnston fonds at University of Victoria, Special Collections
- Denis Johnston at Irish Writers Online
- Denis Johnston at Find a Grave
- Denis Johnston at The Teresa Deevy Archive
- Denis Johnston Irish Playwright page on Facebook
- Denis Johnston on Irish Playography
- Biography on Ricorso
- "The Teresa Deevy Archive".
- "The Teresa Deevy Archive".
- Ronsley, Joseph, ed., Denis Johnston: a retrospective. Irish Literary Studies No. 8, Colin Smythe, Barnes & Noble Books, 1981, p. 5
- New York Times 13 Mar. 1932 sec. 8 p.1
- World Book Encyclopedia, Field Enterprises Educational Corporation, 1959, Vol. 18 p. 8927
- Ronsley op. cit., p. vii
- Let’s Go Britain and Ireland. E.P. Dutton 1986