Along with Gilbert Seldes, Mitchell’s editorship of The Dial magazine signaled a pivotal shift in content from political articles to aesthetics in art and literature.
He resigned his position for political reasons, frustrated that he was forced to give a “politician’s son who should have been flunked” passing grades.
Mitchell returned to the United States and was hired by Scofield Thayer and James Sibley Watson as managing editor of their joint project, The Dial.
In 1922, following two years’ study at the University of Montpellier and Jesus College, Cambridge, he returned to the States and lived with his elderly aunt in New York.
His "naturally keen memory and sharp eye, coupled with a sure ear for words and an occasionally brilliant wit, permitted him to excel."