Born in Ellensburg, Washington, Clymer first studied art through an Art Instruction School correspondence course.
Clymer continued to study art in Canada, where he attended the Vancouver School of Art (now Emily Carr University) and the Ontario College of Art and Design's summer school. He spent eight years illustrating for Canadian magazines.
In Westport, Connecticut, Clymer continued his studies under N.C. Wyeth and the painter and teacher Harvey Dunn and established his career as an illustrator for American magazines, including Argosy, The Saturday Evening Post, Woman's Day and Field and Stream. Clymer created over eighty covers for The Saturday Evening Post.
While in the Marine Corps, he illustrated for Leatherneck Magazine and the Marine Corps Gazette. His work in advertising included paintings for White Horse Scotch Whisky, the Pennsylvania Railroad and the Chrysler Corporation.