Sandys was the son of James Sandys, of Slade House, Stroud, Gloucestershire, and was educated at Clifton College and Pembroke College, Oxford.

[2] After the war ended, he transferred to the 2nd Life Guards in November 1902,[3] leaving the army in 1905.

He rejoined to serve in the British Expeditionary Force in the First World War and was wounded at Ypres.

He later joined the diplomatic service, serving as an Honorary Attaché in the British Legation in Bern (1921–22) and Paris (1922-25).

[4] Duncan became a member of parliament and cabinet minister, and Duncan's daughter Laura Sandys, also a Conservative politician, was elected to represent South Thanet in 2010.