Kennedy was born at Brick Kiln Farm,
Colchester, Essex, the only son of
Lord Angus Kennedy (the third son of
3rd Marquess of Ailsa), and Gertrude Millicent Cooper. He was educated at
Nautical College Pangbourne. In early life, as David Kennedy, he worked as a
steam locomotive fireman and, as Marquess, ran the
Isle of Man Railway as lessee for the 1967–1971 seasons. He was a lieutenant in the
Scots Guards and lieutenant-colonel in the
Royal Scots Fusiliers (
TA). In 1956, his father, Lord Angus, succeeded his childless elder brothers as the 6th
Marquess of Ailsa, at which point Archibald became known by the courtesy title Earl of Cassillis. His father died exactly 365 days later on 1 June 1957, and Archibald succeeded as the 7th Marquess. ==Personal life==