Walker was apprenticed to the photographic firm Notman and Fraser in Toronto. From 1878 he worked in New York City, having a studio there. In 1880 he traveled to Europe and was insipired by the work of the Barbizon painters and rural subject matter occupied him for the rest of his life. Walker was a member of several artists' organizations, including the American Watercolor Society, the Royal Canadian Academy of Art, and the National Academy of Design. He was a founding member of the Canadian Art Club, which elected him as its president in 1915.