The eldest son of Charles, 6th Marquess of Londonderry, and Lady Theresa Chetwynd-Talbot, a daughter of the 19th Earl of Shrewsbury, he was educated at Eton and at the Royal Military College, Sandhurst.

[12][incomplete short citation] In the following months of 1914, Castlereagh extensively witnessed the destruction of war and the terrible suffering of the British wounded.

With his father's death in February 1915, he ceased to be MP for Maidstone and inherited the Londonderry title and the immense wealth and status that went with it.

He served at the front during the Battle of the Somme, witnessing the mass slaughter first-hand; his closest friend, Lieutenant Colonel Harold Brassey, best man at his wedding in 1899, was killed.

[19] For Londonderry, the experiences of war and the carnage of his brother officers and the family and school friends he grew up with would, as Ian Kershaw commented, "leave an indelible mark on him".

His performance earned him high praise, and along with the Londonderrys' role as leading political hosts, he was rewarded by Prime Minister Stanley Baldwin with a seat in the Cabinet in 1928 as First Commissioner of Works.

Londonderry was invited to join the emergency National Government under Prime Minister Ramsay MacDonald and Lord President Baldwin in 1931.

When the National Government won the 1931 General Election he returned to the Cabinet as Secretary of State for Air (Londonderry held a pilot's licence).

[26]: 70  The scenes of Shanghai in flames together with the increasingly assertive Japanese claims about China and the Far East in general as within its sphere of influence convinced Londonderry that Britain needed a strong Royal Air Force as the best way to deter Japan from attacking the British empire and to ensure that Britain was prepared for war should Anglo-Japanese relations take a turn for the worse.

[27]Londonderry toed the British government's equivocal line on disarmament but opposed in Cabinet any moves that would risk the deterrent value of the Royal Air Force.

Ribbentrop is reported to have landed in Newtownards with a "noisy gang of SS men" and the four-day visit became a national newspaper story.

[31] Londonderry entertained Ribbentrop for a further four days at his family home in County Durham, Wynyard Hall on 13–17 November and accompanied him to briefings with government officials in London.

During the first two visits, prior to the abdication of Edward VIII, whom the Nazis assessed as a supporter, Londonderry was considered an aristocrat of real influence by Hitler.

The friendly regard in which Londonderry was held in Berlin was reflected in Hitler indiscreetly informing his guest, in October 1936, of his intended moves both on Czechoslovakia and Poland, years before two invasions happened.

In the end, Londonderry's high-profile promotion of Anglo-German friendship marked him with a far greater slur than what had led him to engage in appeasement in the first place.

Then, after the Munich agreement, in October 1938, Londonderry wrote in a letter that he was aware that Hitler was "gradually getting back to the theories which he evolved in prison", when working on Mein Kampf.

Londonderry's work was openly antisemitic, declaring: "I have no great affection for the Jews ... it is possible to trace their participation in most of the international disturbances which have created so much havoc in different countries.

With talk of his possible internment, Londonderry retreated to Mount Stewart,[35] where he produced Wings of Destiny (1943), a relatively short memoir that was considerably censured by some of his former colleagues, and where he died in 1949.

[citation needed] Having suffered a stroke after a gliding accident a few years after the end of the war, Lord Londonderry died on 10 February 1949 at Mount Stewart, County Down, aged 70.