Born in Loudon, New Hampshire, Walker was a self-taught artist who worked as a commercial wood and steel engraver, also an etcher and painter. Walker claimed to have accidentally discovered the monotype technique as early as 1877, and maintained that he was the "inventor" of the process. He is one of the earliest American artists to concentrate on the monotype, and he exhibited a number of them in Boston in 1881. There was a rivalry between Walker and Albion H. Bicknell, who also took credit for the invention of the monotype. Walker's work is influenced by the then-popular Barbizon School, both in subject and approach. He was very concerned with the play of light on landscape, water and atmosphere. He mostly worked in black and brown tones, but as early as 1883, he had made color monotypes with oil paint. Walker's monotypes were larger in scale than many of his contemporaries' work in the medium. Walker remains one of the seminal figures in the development of the monotype in America. ( Monotypes of the 19th & 20th Centuries, Exh. cat., Frederick Baker Inc., Chicago, 2007.)