Born in St. Louis, Missouri, Barclay received his primary art training at the School of the Art Institute of Chicago and the Art Students League (NYC), where his teachers included George Bridgman and Thomas Fogarty. He was a member of the Artists Guild, the Art Students League of New York, and the Society of Illustrators.
Beginning in his early twenties, Barclay's work appeared in major magazines such at the Saturday Evening Post and the Ladies' Home Journal. His subject was often "the American beauty", the icon of femininity that dominated popular visual culture from the 1890s forward, taking various forms since Charles Dana Gibson debuted his Gibson Girl.
This stock character also played a major role in his numerous national advertisements for a wide variety of products.
Barclay also operated his own firm, for which he designed jewelry and other decorative arts.
During World War I, Barclay won a prize for his 1917 poster "Fill the Breach." In 1918, he designed naval camouflage. He returned to camouflage design during World War II; he also created government posters for the war effort. A naval Lieutenant Commander, Barclay was killed in action when his ship was torpedoed in the Solomon Islands.
