John Granville Cornwallis Eliot, 6th Earl of St Germans, MC was born on 11 June 1890 at 13 Grosvenor Gardens, London to Henry Cornwallis Eliot, 5th Earl of St Germans (11 February 1835 – 24 September 1911) and his wife Emily Harriett Labouchere (24 June 1844 – 18 October 1933).
He was educated at a college in St Peter Intra, Broadstairs, Kent and at the Royal Military College, Sandhurst. He subsequently became a Captain in the 2nd Dragoons of the Scots Greys, and fought in the First World War, being awarded the Military Cross.
He married Lady Blanche Linnie Somerset (15 April 1897 – 30 August 1968), the eldest daughter of the 9th Duke of Beaufort, on 11 June 1918 in London and they had two daughters:
John died on 22 March 1922 from the effects of an accident sustained during a point-to-point race at Wrangton nr Totnes, Devon. As the youngest son with no sons to inherit, his title passed to his first cousin Granville John Eliot, 7th Earl of St Germans (22 September 1867 – 20 November 1942).