He was a member of David Lloyd George's coalition government during the First World War and also served as Ambassador to the United States.

Geddes was born in London as the son of Auckland Campbell-Geddes, a civil engineer, and his wife Christina Helen MacLeod Anderson.

[6] In 1909 he was elected a Fellow of the Royal Society of Edinburgh; his proposers were William Turner, Sir Edward Albert Sharpey-Schafer, David Waterston and George Chrystal.

[14] As His Majesty's ambassador, Geddes investigated the treatment of British immigrants at Ellis Island, for which he wrote a report (1923).

[15] He was also heavily involved in the negotiations that led up to the Washington Naval Treaty of 1922, which limited the size and number of the world's battleships.

[17] On 8 September 1906, Geddes was married to Isabella Gamble Ross (1881–1962) at St. Mary's Church in Livingston, Staten Island.