Politician, banker and landowner. Born in Edinburgh, Duff held senior positions with various banks and was a Member of Parliament for the Liberal Party (1874 - 1879). He married Princess Louise, eldest daughter of King Edward VII, in 1889 at the Chapel in Buckingham Palace. Duff acceded to the Earldom of Fife on the death of his father, James, the 5th Earl (1879), but was created the Duke of Fife in his own right (1900). Unusually, this Dukedom is permitted to pass down the female line if their are no male heirs.
Duff died in Egypt and lies buried at Braemar.