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Chapin was born in West Orange, New Jersey, to James A. Chapin and Delia S. Ryder. He studied at Cooper Union, the Art Students League of New York, and abroad at the Royal Academy of Antwerp, Belgium. Early in his career he won the Temple Gold Medal of the Pennsylvania Academy for his portrayals of the Marvin Family. Chapin executed numerous portraits of well-known public figures; at least five of his portraits were commissioned by TIME as cover art. Other illustrators of Time covers during the period from 1942 to 1966, which has been called the golden age of Time covers, included Boris Artzybasheff, Robert Vickrey, Bernard Safran and Boris Chaliapin.
Chapin's works have been acquired by many private collectors and for the permanent collections of the many institutions such as The Pennsylvania Academy of Fine Arts (where he taught portraiture), The Phillips Collection, The Art Institute of Chicago, The Newark Museum, Amherst College, The Dallas Museum of Art, Texas; The Asheville Art Museum, The Currier Gallery of Art, The Five College Museums Collections, The Harvard Art Museums, and The Indianapolis Museum of Art.
While teaching in California in the late 1930s, Chapin met Mary Fischer; they married soon after. Largely due to his opposition to United States foreign policy in Southeast Asia, he moved to Canada in 1969, and died in Toronto in 1975.