Completing his work for a Ph.D. degree at Columbia and encouraged by John Dewey, he taught logic for three years at the University. In 1909 Eastman organized the Men's League for Woman's Suffrage. His marriage to Ida Rauh, actress and poet, occurred in 1911 and produced comment when it was learned Miss Rauh would retain her maiden name. Their son Daniel was born in 1912. A year later Eastman's first books, Enjoyment of Poetry and Child of the Amazons, were published. During this time he became editor of The Masses with its new idea in format and inclination toward then-radical causes and worked with it until its close in October, 1917. The next year with his sister Crystal Eastman as co-owner he started a new periodical with similar interests called The Liberator.

Leaving The Liberator in the hands of others in 1922 Eastman attended the International Conference at Genoa, Italy, where he met the secretary to Maxim Litvinoff, Eliena Krylenko, 1895-1956, artist and dancer. Continuing on to Russia the two met again and were married in 1924. Their correspondence may be found in the Eastman, E., mss. (The divorce from Miss Rauh had been effected in 1922). During a sojourn of five years in Europe Eastman became acquainted with Leon Trotsky, served as his literary agent in the United States, and translated some of his works. The correspondence for this relationship may be found in the Trotskii mss. Pursuing his interests in writing and lecturing on Russia, socialism, literature, humor, and poetry, Eastman became engaged as a roving editor for The Reader's Digest Association for a number of years.

Following Eliena Krylenko Eastman's death in 1956, Eastman married Yvette Szekely, a former social worker, in 1958. Szekely Eastman (whose name also appears as Sekey and Sekely) moved from Budapest to New York with her stepmother Margaret, a self-made ladies' undergarment designer and journalist, and her sister Sue at a young age. Through her stepmother's journalistic connections, Szekely Eastman met and was romantically involved with author Theodore Dreiser, through whose social circles she also met Max Eastman. An avid photographer, Szekely Eastman enjoyed traveling and regularly visited her mother Marthe in Geneva, Switzerland. Further biographical information about Yvette Szekely Eastman can be found in her memoir, Dearest Wilding.