[1][2] Hardinge entered the diplomatic service in 1880, and was attached to the embassy in Constantinople, where he was private secretary to the ambassador Lord Dufferin.

As chargé d′affairs in Bucharest he was involved in negotiating a treaty and a trade marks convention between the United Kingdom and Romania.

Although Hardinge was the target of assassination attempts with bomb attack by the Indian nationalists Rash Behari Bose and Sachin Sanyal, his tenure included an improvement of relations between the British administration and the nationalists, as a consequence of the implementation of the Morley-Minto reforms of 1909, and of Hardinge's own admiration for Mohandas Gandhi and criticism of the South African government's anti-Indian immigration policies.

In particular, the British Indian Army played a significant (though initially mismanaged) role in the Mesopotamian campaign.

[7] In 1916, Hardinge returned to his former post in England as Permanent Under-Secretary at the Foreign Office,[4] serving with Arthur Balfour.

Edward Hardinge, died 18 December 1914, aged 22, from wounds while serving as a Lieutenant with the 15th (The King's) Hussars in France.

[10] Diamond Hardinge was a bridesmaid at the wedding of Prince Albert, Duke of York, and Lady Elizabeth Bowes-Lyon on 3 May 1923.