Dennis Yeats Wheatley was born in South London to Albert David and Florence Elizabeth Harriet Wheatley (née Baker). He was the eldest of three children of an upper middle class family, the owners of Wheatley & Son of Mayfair, a wine business. He was expelled from Dulwich College. Following his expulsion Wheatley became a Merchant Navy officer cadet on the training ship HMS Worcester.

He took part in the First World War but was gassed in a chlorine attack at Passchendaele and invalided out as a second lieutenant in the Royal Field Artillery after seeing service in Flanders, on the Ypres Salient, and in France at Cambrai and St. Quentin. He took over the family wine merchant business in 1919, but following a decline in business after the depression in 1931, he set about writing and married his second wife.

During the Second World War, Wheatley's literary talents led him onto planning staffs for the War Office. He wrote numerous papers for the War Office, including drawing up suggestions for dealing with a German invasion of Britain (recounted in his work "Stranger than Fiction"). The most famous of his submissions to the Joint Planning Staff of the war cabinet was on "Total War". He was given a commission directly into the JPS as Wing Commander, RAFVR and took part in advanced planning for the Normandy invasions.

His first book, Three Inquisitive People, was not immediately published; but his first published novel, The Forbidden Territory, was an immediate success when published in 1933, being reprinted seven times in seven weeks.

He wrote adventure stories, with many books in a series of linked works. His plots covered the French Revolution (Roger Brook Series), Satanism (Duke de Richleau), World War II (Gregory Sallust) and espionage (Julian Day).

In the thirties, he conceived a series of whodunit mysteries, presented as case files, with testimonies, letters, pieces of evidence such as hairs or pills. The reader had to go through the evidence to solve the mystery before unsealing the last pages of the file, which gave the answer. Four of these 'Crime Dossiers' were published: Murder Off Miami, Who Killed Robert Prentice, The Malinsay Massacre, and Herewith The Clues.

In the 1960s his publishers were selling a million copies of his books per year. A small number of his books were made into films by Hammer, of which the best known is The Devil Rides Out (book 1934, film 1968). His writing is very descriptive and in many works he manages to introduce his characters into real events while meeting real people. For example, in the Roger Brook series the main character involves himself with Napoleon, and Joséphine whilst being a spy for the Prime Minister William Pitt. Similarly, in the Gregory Sallust series, Sallust shares an evening meal with Hermann Göring.

He also wrote non-fiction works, including accounts of the Russian Revolution and King Charles II, and his autobiography. He was considered an authority on the supernatural, satanism, the practice of exorcism, and black magic, to all of which he was hostile. During his study of the paranormal, though, he joined the Ghost Club.

From 1974 through 1977 he edited a series of 45 paperback reprints for the British publisher Sphere under the heading "The Dennis Wheatley Library of the Occult", selecting the titles and writing short introductions for each book. This series included both occult-themed novels by the likes of Bram Stoker and Aleister Crowley (with whom he once shared a lunch) and non-fiction works on magic, occultism, and divination by authors such as the Theosophist H. P. Blavatsky, the historian Maurice Magre, the magician Isaac Bonewits, and the palm-reader Cheiro.

Two weeks before his death in November 1977, Wheatley received conditional absolution from his old friend Cyril ‘Bobby’ Eastaugh, the Bishop of Peterborough.

His estate library was sold in a catalogue sale by Basil Blackwell's in the 1970s, indicating a thoroughly well-read individual with wide-ranging interests particularly in historical fiction and Europe. His influence has declined, partly due to difficulties in reprinting his works owing to copyright problems.

Fifty-two of Wheatley's novels were published posthumously in a set by Heron Books UK.More recently, in April 2008 Dennis Wheatley's literary estate was acquired by media company Chorion.

He invented a number of board games including Invasion .

He was cremated at Tooting and his ashes interred at Brookwood Cemetery. He is commemorated on the Baker/Yates family monument at West Norwood Cemetery.

His grandson Dominic Wheatley went on to become one of the co-founders of the software house Domark, which published a number of titles throughout the 1980s and 1990s.

His work is fairly typical of his class and era, portraying a way of life and ethos of clubland snobbery that gives an insight into the values of the time, good and bad. His leading characters are all dyed-in-the-wool supporters of Royalty, Empire and the class system and many of his villains are villainous because they attack these ideas, although in The Golden Spaniard he pits various protagonists against each other in the setting of the Spanish Civil War. His works are enjoyable thrillers, and his "Roger Brook" series in particular offer the reader "history without tears" (Wheatley, in the introduction to The Man Who Killed the King). His historical analysis is coloured by his politics, but is well informed. For example, Vendetta in Spain (pre-WWI adventure in that country) contains a discussion of political anarchism which is well grounded, though unsympathetic. His strong attachment to personal liberty also informs much of his work. This, as well as a sympathetic attitude toward Jews (as shown in the 'Simon Aron' character introduced in 'Three Inquisitive People') led him to mercilessly flay the Nazi system in those 'Gregory Sallust' thrillers set in World War Two.

In the winter of 1947 Wheatley penned 'A Letter to Posterity' which he buried in an urn at his country home. The letter was intended to be discovered some time in the future (but was found in 1969 when that home was demolished for redevelopment of the property). In it he predicted that the socialist reforms introduced by the post-war government would inevitably lead to an unjust state, and called for both passive and active resistance to it.

"Socialist ‘planning’ forbids any man to kill his own sheep or pig, cut down his own tree, put up a wooden shelf in his own house, build a shack in his garden, and either buy or sell the great majority of commodities — without a permit. In fact, it makes all individual effort an offence against the state. Therefore, this Dictatorship of the Proletariat, instead of gradually improving the conditions in which the lower classes live, as has been the aim of all past governments, must result in reducing everyone outside the party machine to the level of the lowest, idlest and most incompetent worker.

[...]

It will be immensely difficult to break the stranglehold of the machine, but it can be done, little by little; the first step being the formation of secret groups of friends for free discussion. Then numbers of people can begin systematically to break small regulations, and so to larger ones with passive resistance by groups of people pledged to stand together — and eventually the boycotting, or ambushing and killing of unjust tyrannous officials."

:Dennis Wheatley, A Letter to Posterity

• The Forbidden Territory 1933
• Such Power is Dangerous 1933
• 'Old Rowley' 1933
• Black August 1934
• The Fabulous Valley 1934
• The Devil Rides Out 1934
• The Eunuch of Stamboul 1935
• They Found Atlantis 1936
• Murder Off Miami 1936
• Contraband 1936
• The Secret War 1937
• Who Killed Robert Prentice? 1937
• Red Eagle 1937
• Uncharted Seas 1938 (filmed as The Lost Continent)
• The Malinsay Massacre 1938
• The Golden Spaniard 1938
• The Quest of Julian Day 1939
• Herewith the Clues 1939
• Sixty Days to Live 1939
• The Scarlet Impostor 1940
• Three Inquisitive People 1940
• Faked Passports 1940
• The Black Baroness 1940
• Strange Conflict 1941
• The Sword of Fate 1941
• Total War 1941
• V for Vengeance 1942
• Mediterranean Nights 1942
• Gunmen, Gallants and Ghosts 1943
• The Man Who Missed the War 1945
• Codeword Golden Fleece 1946
• Come into My Parlour 1946
• The Launching of Roger Brook 1947
• The Shadow of Tyburn Tree 1948
• The Haunting of Toby Jugg 1948
• The Rising Storm 1949
• The Seven Ages of Justerinis 1949

• The Second Seal 1950
• The Man Who Killed the King 1951
• The Star of Ill Omen 1952
• To the Devil - a Daughter 1953
• Curtain of Fear 1953
• The Island Where Time Stands Still 1954
• The Dark Secret of Josephine 1955
• The Ka of Gifford Hillary 1956
• The Prisoner in the Mask 1957
• Traitors' Gate 1958
• Stranger than Fiction 1959
• The Rape of Venice 1959
• The Satanist 1960
• Saturdays with Bricks 1961
• Vendetta in Spain 1961
• Mayhem in Greece 1962
• Gunmen,Gallants and Ghosts (rev.) 1963
• Mediterranean Nights (rev.) 1963
• The Sultan's Daughter 1963
• Bill for the Use of a Body 1964
• They Used Dark Forces 1964
• Dangerous Inheritance 1965
• The Eight Ages of Justerinis 1965
• The Wanton Princess 1966
• Unholy Crusade 1967
• The White Witch of the South Seas 1968
• Evil in a Mask 1969
• Gateway to Hell 1970
• The Ravishing of Lady Mary Ware 1971
• The Devil and all His Works 1971
• The Strange Story of Linda Lee 1972
• The Irish Witch 1973
• Desperate Measures 1974
• The Young Man Said 1977
• Officer and Temporary Gentleman 1978
• Drink and Ink 1979
• The Deception Planners 1980

Baker, Phil, The Devil is a Gentleman: the Life and Times of Dennis Wheatley, Sawtry, UK: Dedalus. 2009. ISBN 9781903517758