(Alfred) Duff Cooper was born in February 1890, the son of Sir Alfred Cooper and Lady Agnes Cecil Emmeline Flower. He was educated at Eton College and New College, Oxford.

In October 1913 he joined the Foreign Office but was released in June 1917 to join the army as a Subaltern in the Grenadier Guards. He spent only six months at the front, but earned the DSO. He subsequently returned to the Foreign Office and after a period in the Egyptian Department was appointed as Private Secretary to the Parliamentary Under-Secretary.

In June 1919, despite initial opposition from her family, he had married Lady Diana Manners, daughter of the 8th Duke of Rutland. Diana received a substantial windfall in 1923 from her role as the Madonna in Max Reinhardt's pantomime "The Miracle". This allowed Duff Cooper to leave the Foreign Office in July 1924 and his adoption as Conservative candidate for the (two-member) constituency of Oldham where he was elected an MP.

In January 1928 he was appointed Financial Secretary to the War Office, but in the General Election of the Spring of 1929 he lost his seat and the Conservatives lost power. In March 1931 Duff Cooper was again elected to the Commons after a by-election in the St George's Division of Westminster. He was subsequently appointed as Under-Secretary at the War Office and, in June 1934, as Financial Secretary to the Treasury. After the General Election of November 1935 Cooper entered the Cabinet as Secretary of State for War and was sworn into the Privy Council.

Cooper was seen as one of the few members of the Cabinet who were supportive of Edward VIII during the abdication crisis of 1936 and was prepared to contemplate the possibility of a morganatic marriage. In September 1936 he and Diana Cooper joined the King and Mrs Simpson for a Mediterranean cruise (see DUFC 2/17).

In May 1937 Neville Chamberlain as Prime Minister invited Cooper to become First Lord of the Admiralty. However he resigned from the Government in October 1938 after the Munich agreement, which he denounced in the House of Commons. Cooper had earlier in the 1930s visited Germany and had attended a Nuremberg rally. On the outbreak of World War Two he set out for a lecture in the United States. After Churchill became Prime Minister Cooper was appointed Minister of information in May 1940 and then, in July 1941, as Chancellor of the Duchy of Lancaster.

Cooper was then posted to Singapore as Resident Cabinet minister with responsibility for Far Eastern affairs. He was authorized to form a war cabinet but found neither the civil nor the military authorities inclined to accept his leadership and was pleased when Wavell's appointment as Supreme commander in the South West Pacific meant he could return to Britain. For the next eighteen months he served as Chairman of the Cabinet Committee on Security.

In December 1943 he was appointed as the British representative to the French Committee of National Liberation in Algiers, with the understanding that he would be the Ambassador in Paris when this possible. His main responsibility was to develop a working partnership with the Free French leader, General de Gaulle. In September 1944 Cooper moved to Paris, and he served as Ambassador until 1948. In March 1947 he helped secure a treaty of alliance between Britain and France at Dunkirk. In their retirement the Coopers lived at Chantilly.

Cooper's published works included a book on the French statesman Talleyrand which was published in 1932, a two volume official biography of Field Marshal Earl Haig (1935 & 1936), a wartime life of the Old Testament figure King David, "Sergeant Shakespeare" (1949) a novel, "Operation Heartbreak" (1950), based on a real-life incident in the Second World War and his autobiography, "Old Men Forget" (1953). In 1948 he was awarded GCMG and, in July 1952, elevated to the peerage as 1st Viscount Norwich. He died in January 1954 and was succeeded by his son, John Julius.