By the age of 15 he was submitting cartoons to the local magazine The Wizard of the North[citation needed] and was later taken on as an assistant in the art department of the Dundee Advertiser.
Most of his income at this time was derived from portrait commissions, including the jute merchant John L. Luke and Mrs Hunter of Hilton.
As part of the Celtic Revival movement, Duncan painted murals for Geddes's halls of residence at Ramsay Garden.
He also created Dundee's first design collective by gathering together a group of young talents who created and exhibited decorative art and design pieces for the Graphic Arts Association, including Nell Baxter, Rosa Baxter, Elizabeth Burt and Duncan's sister Jessie Westbrook.
[3] Thanks to Patrick Geddes's influence, in 1900 Duncan was appointed as a Professor at the Chicago Institute founded by Francis Wayland Parker.