Born in 1865, he succeeded as the 4th Earl Cairns on the death of his older brother, Herbert, in 1905.
After retiring, he was on 9 February 1898 appointed a major of the 5th (Militia) battalion, previously the Queen's Own Royal Tower Hamlets Light Infantry (2nd Tower Hamlets Militia), based in Bethnal Green in the East End of London.
Following the outbreak of the Second Boer War, Cairns volunteers for service when his militia regiment was embodied in 1900.
After peace was declared in May 1902, he left South Africa on board the SS Bavarian and arrived in the United Kingdom the following month.
Their youngest daughter, Katharine, was a Senior Commander in the Auxiliary Territorial Service.