He evolved from radical Marxist penning political essays to highly respected literary critic.
In the 1930s, he was a Marxist radical, whose circle included: Robert Cantwell, Edmund Wilson, Malcolm Cowley, John Chamberlain, Erskine Caldwell, Matthew Josephson, Harry Hansen, James T. Farrell, Meyer Schapiro, John Dos Passos, Newton Arvin, Kenneth Burke, Granville Hicks, Kenneth Fearing, and Whittaker Chambers.
With Cantwell and others, Dupee held an abiding interest in Henry James.
Dupee was a Marxist, and an organizer for the Communist Party in New York City in the mid-1930s.
By 1937 he had had become disillusioned with the party, although he maintained his socialist thought and activism for the rest of his life.