Originally from Glasgow, Duncan relocated to London sometime in 1899 or so. Not much is known of him in the literature, but he seems to have been primarily a designer for books and greeting cards.
He is also referenced in A.W. Coysh's "The dictionary of picture postcards in Britain, 1894-1939" as using the pseudonym "Hamish" for postcard designs. It is unknown if he used this pseudonym for his bookwork as well.
He designed book covers and title pages for a number of London or Edinburgh based publishers, including John Long, Sands & Co., and Oliphant Anderson & Ferrier.
Where his designs appear on books by American publishers, it is a repeat of the design used by the UK edition of that same book. As far as I know, he has not designed any covers specifically for American imprints.