Denis Sefton Delmer was born in Berlin, Germany, on 24th May 1904. His father, Frederick Delmer, was an Australian lecturer in English at Berlin University and on the outbreak of the First World War was interned as an enemy alien. In 1917 Delmer and his family were allowed to go to England.
Delmer was educated at Lincoln College, Oxford, where he obtained a second class degree in German. After leaving university he worked as a freelance journalist until being recruited by the Daily Express to become head of its new Berlin Bureau. While in Germany he became friendly with Ernst Roehm and he arranged for him to become the first British journalist to interview Adolf Hitler. In the 1932 general election Delmer travelled with Hitler on his private aircraft. He was also with Hitler when he inspected the Reichstag Fire. During this period Delmer was criticized for being a Nazi sympathizer and for a time the British government thought he was in the pay of the Nazi regime.
In 1933 Delmer was sent to France as head of the Daily Express Paris Bureau. He also covered important stories in Europe including the Spanish Civil War and the invasion of Poland by the German Army in 1939. He also reported on the German Western Offensive in 1940.
Delmer returned to England and in September 1940 he was recruited by the Special Operations Executive (SOE) to organize 'Black Propaganda' broadcasts to Nazi Germany. This included Soldatensender Calais, a pseudo-German radio station established in Crowborough for the German armed forces. Delmer's propaganda stories included spreading rumours that foreign workers were sleeping with the wives of German soldiers serving overseas. When Stafford Cripps discovered what Delmer was up to he wrote to Anthony Eden, the foreign secretary: "If this is the sort of thing that is needed to win the war, why, I'd rather lose it."
After the Second World War Delmer became chief foreign affairs reporter for the Daily Express. Over the next fifteen years Delmer covered nearly every major foreign news story for the newspaper. However, rumours began to circulate that Delmer was spying for the Soviet Union.
Lord Beaverbrook sacked Delmer in 1959 and he retired to Suffolk where he wrote two volumes of autobiography, Trial Sinister (1961), Black Boomerang (1962) and several other books including Weimar Germany (1972) and The Counterfeit Spy (1973).
Sefton Delmer died at Lamarsh, Suffolk, on 4th September 1979.