The magazine featured reportage, poetry, art and fiction, and sponsored the John Reed Club, and American Writers and Artists Congresses.

The main editorial staff comprised Mike Gold, Hugo Gellert, John F. Sloan, Max Eastman, Joseph Freeman, Granville Hicks, Walt Carmon, and James Rorty.

Writers that regularly contributed to New Masses include Max Eastman, William Carlos Williams, John L. Spivak, Theodore Dreiser, John Dos Passos, Floyd Dell, Agnes Smedley, Upton Sinclair, Richard Wright, Waldo Frank, Albert Maltz, Joseph North, Carl Sandburg, Ralph Ellison, James Agee, Alvah Bessie, Erskine Caldwell, Sherwood Anderson, Dorothy Parker, Dorothy Day, John Breecher, Langston Hughes, Eugene O’Neill, Rex Stout, and Ernest Hemingway.

The graphic design and art of New Masses was groundbreaking in its day, and features artwork from Kenneth Fearing, H.H. Lewis, Jack Conroy, Grace Lumpkin, Jan Matulka, Ruth McKenney, Maxwell Bodenheim, Meridel LeSueur, Josephine Herbst, Jacob Burck, Tillie Olsen, Stanley Burnshaw, Louis Zukofsky, Art Young, George Oppen, Wanda Gag, Albert Halper, Al Hirschfeld, and William Gropper, among others.