After leaving Malcom's employ, Wheeler-Bennett served in the publicity department of the League of Nations in 1923-1924 in Geneva. Afterwards, Wheeler-Bennett worked as the director of the Royal Institute of International Affairs' information department. In particular, Wheeler-Bennett worked as the editor of the Bulletin of International News between 1924-1932.
In 1933, Wheeler-Bennett told the Royal Institute of International Affairs that:
Wheeler-Bennet's biography of Paul von Hindenburg created his reputation as a historian. Another great success was The Forgotten Peace, a study of the Treaty of Brest-Litovsk. This is still regarded as the standard historical study of the subject.
After the Second World War, Wheeler-Bennett was a critic of Appeasement and 10 years after the Munich Agreement wrote a book condemning it.
In the pre-1939 period, Wheeler-Bennett befriended or was at least on speaking terms with a number of well-known people all over Europe. Some of the people he had some contact with included Heinrich Brüning, Basil Liddell Hart, Franz von Papen, John Buchan, Carl Friedrich Goerdeler,Leon Trotsky, Hans von Seeckt, Max Hoffmann, Lewis Bernstein Namier, Benito Mussolini, Robert Bruce Lockhart, Karl Radek, Sir Robert Gilbert Vansittart, Kurt von Schleicher, Sir Isaiah Berlin, Tomáš Masaryk, Engelbert Dollfuss, the former Kaiser Wilhelm II, Adam von Trott zu Solz, Louis Barthou, Lord Lothian, Winston Churchill, and Dr. Edvard Beneš.
From 1940 onwards, he worked with the British Information Service in New York City, an agency charged with trying to persuade the United States to enter the war on the Allied side. Whilst here, he was a supporter of the German Resistance to Hitler and became friendly with Adam von Trott zu Solz.
Starting in 1942, Wheeler-Bennett worked in the Political Warfare department of the British Foreign Office in London. After he joined the Foreign Office, he switched to being an opponent of the German Resistance, his change being described by the biographer Anthony Howard, in the New Statesman, as "one of the most nimble political somersaults the corridors of power can ever have seen". Wheeler-Bennett gained his reward, being promoted to the Assistant Director General of Political Intelligence Department before going on to serve in the Political Adviser's Department in SHAEF in 1944-1945. In 1945-1946, Wheeler-Bennett assisted the British Prosecution at the Nuremberg Trials.
Wheeler-Bennett's views on Germany and the German Resistance caused unease to some of his wartime colleagues, an internal February 1944 paper of his being condemned by Professor Thomas Marshall - of the Foreign Office Research Department - as a "vitriolic little paper" and "hardly worthy of its distinguished author." (British National Archives file FO 371/39137)
After the Second World War, he was the British editor-in-chief of the German Foreign Ministry's archives and oversaw the early publications of the German Documents on Foreign Affairs from 1946-1948. From 1948-1956, he served as the Historical Adviser to the Foreign Office Project for publishing the German Foreign Ministry Archives. In these roles, he did his best to suppress any material which was embarrassing either for him personally, or for the Foreign Office. He was particularly sensitive to papers mentioning British contacts with the German Resistance, or containing any evidence that German Resistance members saw their actions as required by their sense of ethics or morality.
He was appointed as official biographer of King George VI, after the King's death in 1952, producing a biography which appeared in 1958. Historian David Cannadine in History In Our Time criticised Wheeler-Bennett's book as "courtly and obsequious," the history "of an icon rather than of an individual," and a "sanitised sarcophagus."
His thesis was that under von Seeckt's leadership during the Weimar period, the Reichswehr formed a "State within the State" that largely preserved its autonomy from the politicians in Berlin, but that it did not, however, play an active role in day-to-day politics.
After von Seeckt's downfall in 1926, which had been engineered by Schleicher, the Reichswehr became increasingly engaged in political intrigues. In Wheeler-Bennett's view, Schleicher was the "Gravedigger of the Weimar Republic" who succeeded in undermining democracy, but failed completely to build any sort of stable structure in its place. Thus by a mixture of cunning, intrigue and inept manoeuvres, Schleicher inadvertently paved the way for Adolf Hitler.
In the revised 1964 edition of The Nemesis of Power, Wheeler-Bennett continued his story right up to the July 20 Plot of 1944. He contended that under the leadership of Werner von Blomberg and Werner von Fritsch, the German Army chose to acquiesce in the Nazi regime as the kind of government best able to achieve what the Army wanted; namely a militarized society that would ensure in the next war that there would be no repeat of the “stab in the back”.
By agreeing to support the Nazi dictatorship, the Army tolerated a regime that quietly and gradually dismantled the “State within the state”. After Blomberg's and Fritsch's fall in 1938, the Army increasingly became just a tool of the Nazi regime rather than the independent actor that it had been before. Despite his hostility to the German generals, Wheeler-Bennett in the book acknowledged the courage of men such as Claus von Stauffenberg. Overall, he concluded that the conservative opposition within the Wehrmacht had done too little, too late to overthrow the Nazis.
He was a follower of the Great Man school of history and his writings usually explained historical events in terms of the leading personalities of the period under study. This view of history together with his own right-wing outlook led him to make Churchill the principal hero of his writings.
Sir John Wheeler-Bennett died of cancer in London on 9 December, 1975, aged 73.
He was very well known in his lifetime and his interpretation of the role of the German Army influenced some British historians. However, he is largely forgotten today.