His father, Captain Hugh Mitchell (1849–1937) had served in the Royal Engineers and, after retiring, studied law at the Inner Temple and became a barrister.

[2] His mother, Mary Catherine née Creswell, died when he was two years old,[3] and his father moved to Gibraltar where he built up his legal practice, living at Campamento in Spain.

[9] As Tanganyika Secretary for Native Affairs, in 1929 Mitchell supported cooperatives, and claimed that "in a sense every Bantu village is in fact a co-operative society".

[10] Some members of the colonial office decried him as being "too much of a native sympathizer," however the British governor of Tanganyika Donald Charles Cameron, said that this made him "very effective" and that "men of his sentiments are precisely what is needed.

[17] Mitchell was also British High Commissioner in the Western Pacific, and a large part of his job was to smooth out differences between the allied forces in the struggle with Japan.

Although the white and Fijian people were on good terms and often intermarried, there were tensions with the large Indian population, most of whom were descendants of indentured labourers.

[17] Another issue was that, while the Fijian people were happy to belong to the British Empire, many of the Indians were in sympathy with the independence movement in India and could not be called loyal subjects.

Their reason was that they needed more time to develop experience in local government, or they would be dominated by the Indians.

[19] Even while the Gilbert and Ellice Islands were under Japanese occupation, Mitchell was in charge of planning for the colony's future after the British regained control.

Mitchell died at the Royal Naval Hospital in Gibraltar on 11 October 1964 from heart failure, aged 74.

[23] Talking, after his retirement, of the lack of planning in the early days in East Africa, Mitchell said "there was no colonial policy, for Secretaries of State changed every eighteen months or so; so no one ever disciplined a Governor and no Secretary of State would ever force a row with settlers".

In The Agrarian Problem in Kenya he said of Africans: "They are a people who, however much natural ability and however admirable attributes they may possess, are without a history, culture or religion of their own and in that they are, as far as I know, unique in the modern world.