[1] He was the only son of society doctor Sir Alfred Cooper (1843–1908), a surgeon who specialised in the sexual diseases of the upper classes (his carriage was humorously known as "Cooper's Clap Trap") and Lady Agnes Duff, daughter of James Duff, 5th Earl Fife and descendant of King William IV.

[1] Owing to the national importance of his work at the cipher desk, he was exempted from military service until June 1917, when he joined the Grenadier Guards.

[3] Cooper spent six months on the Western Front, during which, Philip Ziegler writes, he proved himself "exceptionally courageous, resourceful, and a natural leader of men", at a time when the life expectancy of junior officers was very brief.

He suffered a minor wound in the advance to the Albert Canal in August 1918, and was awarded the Distinguished Service Order (DSO) for conspicuous gallantry, a rare decoration for a junior officer.

[4]Almost all his closest friends, including Shaw-Stewart, Horner and Asquith were killed in the war, allowing him to draw closer to Lady Diana Manners, a socialite who was known for her eccentricities.

[6] These included the Franco-American Singer sewing-machine heiress Daisy Fellowes, the socialite Gloria Guinness, the French novelist Louise Leveque de Vilmorin and the writer Susan Mary Alsop (then an American diplomat's wife, by whom he had an illegitimate son, William Patten Jr, who later fathered W. Samuel Patten).

[13] Cooper was a stalwart supporter of Prime Minister Stanley Baldwin, and a friend of Chancellor of the Exchequer, Winston Churchill.

[15] The March 1931 by-election for the constituency of Westminster St George's (caused by the death of Cooper's recent boss, Laming Worthington-Evans), saw Beaverbrook's Empire Free Trade Crusade party threatening the Conservative position at a time when satisfaction with Baldwin's leadership was at a low.

When the original Conservative candidate, John Moore-Brabazon, stepped down, Duff Cooper agreed to contest the election in what was regarded as a referendum on Baldwin's leadership.

[6] In August 1931, on the formation of the National Government, he was appointed Financial Secretary to the War Office under the elderly Lord Crewe, who left Cooper to do a great deal of the work.

The book received many generous reviews and remained the leading biography of Haig until John Terraine's The Educated Soldier in 1963.

[17] At that time Cooper admitted to Robert Blake, the editor of that work, that he had been influenced by the politics of the 1930s and the desire to facilitate Anglo-French rapprochement.

[6] In November 1935, after the general election, Cooper was promoted to the Cabinet as Secretary of State for War and appointed to the Privy Council.

[18] During the Abdication Crisis he was sympathetic to Edward VIII and to the possibility of a morganatic marriage, and in vain advised him to wait until after his coronation (due in 1937) before picking a fight with the government over his plans to marry Wallis Simpson.

[19] He felt out of kilter with the Conservative leadership and was surprised when the new Prime Minister Neville Chamberlain appointed him First Lord of the Admiralty in May 1937.

[20] He enjoyed high living on board the Admiralty yacht HMS Enchantress, but fought Chamberlain and the Chancellor of the Exchequer Sir John Simon for more spending on the Royal Navy.

[22] Fellow appeasement-critic and Conservative Party MP Vyvyan Adams described Cooper's actions as "the first step in the road back to national sanity".

[23] As a backbencher, he joined the coterie around Anthony Eden (who had resigned as Foreign Secretary in February 1938), but made only muted criticisms of the Government.

[29] He was one of a number of Churchill's proteges promoted in the July 1941 reshuffle: Duncan Sandys became Financial Secretary at the War Office and Brendan Bracken became Minister of Information.

Cuthbert Headlam wrote of Cooper at this time that "he has failed in every job he has been given, is clearly incompetent as an administrator, but belongs to the Winston clique.

In the meantime he chaired the Cabinet Committee on Security, and did a lot of writing, spending his weekends at Bognor where his wife had a smallholding.

His remit included maintaining a working relationship between Churchill and de Gaulle, two men whom he found equally difficult.

[32] He was to prove a very popular ambassador, with Lady Diana helping to make his term of office a great social success.

[20] In the words of the British historian P. M. H. Bell, Cooper was such a "devoted Francophile" that during his time as ambassador to Paris he often tried the patience of the Foreign Office by going well beyond his instructions to maintain good relations with France by trying to create an Anglo-French alliance that would dominate post-war Europe.

[citation needed] Cooper's sixth and final book was his acclaimed memoirs, Old Men Forget, which appeared on 5 July 1953.

[citation needed] This resulted in his suffering a fatal gastro-intestinal hæmorrhage on 31 December 1953 when he was on board the French liner Colombie.

[40] His biographer Ziegler wrote that Cooper was "not totally successful in worldly terms but never dull", though he was "arrogant, self-indulgent and selfish, and devoted far too much time and energy to wine, women and gambling".

[36] On 28 November 2021, Cooper was posthumously awarded the Order of the White Lion, the highest decoration of Czechoslovakia and the Czech Republic, in recognition of his opposition to the Munich Agreement.

[41][42] H. G. Wells, in The Shape of Things to Come which was published in 1934, predicted a Second World War in which Britain would not participate but would vainly try to effect a peaceful compromise.

[43] Cooper was married to Lady Diana from 1919 to his death and their only child was John Julius Norwich (1929–2018), who became well known as a writer and television presenter.