John was educated at Harrow School in England.
Jennie"s sisters believed that John"s actual biological father was Evelyn Boscawen. Lady Gwendoline was a Roman Catholic, as her father had converted before her birth. He was commissioned into the Queen"s Own Oxfordshire Hussars in 1898.
He served in the South African Light Horse alongside his war correspondent brother in the Second Boer War in 1899–1900.
He was Mentioned in Dispatches, and was shot through the leg during the Battle of the Tugela Heights, part of the campaign for the relief of Ladysmith. He fought in World War I, where he was again Mentioned in Dispatches.
He served on the staff of Field Marshal Lord French, General Sir Ian Hamilton (serving as Naval Liaison Officer for the Mediterranean Expeditionary Force) and Field Marshal Lord Birdwood (serving as Camp Commandant, 1st Anzac Corps, and then as Assistant Military Secretary at the headquarters of the Fifth Army). After the war, he became a businessman in the City of London.
During World World War II, the widowed John lost his house during the Blitz and he lived in 10 Downing Street.