Raised in Denver, Hallowell attended Phillips Academy and Harvard University, where he served as editor of the Lampoon. The writer John Reed was a good friend. After graduation Hallowell worked as an illustrator until he teamed up with Walter Lippmann and Herbert Croly to found The New Republic, where he served in many roles, including editor, until 1925. Starting in the mid-1920s, Hallowell dedicated himself to painting, traveling through Europe to familiarize himself with the latest art movements there. He found rapid success, debuting his work in solo shows at the Galerie Bernheim-Jeune in Paris and the Montross Gallery in 1924. He showed regularly in New York and in major exhibitions around the United States through the 1930s. During the Depression he worked for the Federal Art Project and was painting a mural for a post office at the time of his death in 1939.
