His elder brother, Walter Henry, Earl of Dalkeith, was killed in a deer-hunting accident in Achnacary Forest, at the age of 25.

In 1881, he served as a Midshipman in the Royal Navy onboard HMS Bacchante with the grandsons of Queen Victoria – Prince Albert Victor, Duke of Clarence and Avondale and Prince George of Wales, later George V of the United Kingdom.

Buccleuch held the following posts: On Monday 30 January 1893, John married at St Paul's Church, Knightsbridge Lady Margaret Alice "Molly" Bridgeman (20 January 1872 – 7 August 1954), daughter of George Bridgeman, 4th Earl of Bradford, and Lady Ida Frances Annabella Lumley, daughter of Richard Lumley, 9th Earl of Scarbrough.

They had eight children: Buccleuch died from cancer[4] at Bowhill House, Selkirkshire, Borders, Scotland, on 19 October 1935, aged 71, less than a month before his daughter Alice married Prince Henry, the third son of King George V and Queen Mary.

The marriage was to take place at Westminster Abbey, but given the circumstances, the event was scaled back and the venue changed to Buckingham Palace.