As a teaching fellow at Harvard, he shared an office and friendship with Henry Kissinger, later to receive the Nobel Peace Prize as U.S. Secretary of State.
Upon earning his doctorate, Manshel was awarded Harvard's prestigious 1952 Chase Prize in International Relations for the "most publishable document advancing peace" for his preemptive, scholarly work on the unification of post-war Europe.
Shortly after Harvard, Manshel became director and chief administrative officer at the Council for Cultural Freedom, an anti-Communist organization of American and European intellectuals (1954-1955).
During Warren Manshel's tenure as its publisher, The Public Interest gave voice to leading and emerging intellectuals, including Seymour Martin Lipset, Peter Drucker, Leon Kass, Daniel Patrick Moynihan and Francis Fukuyama.
In 1970, Manshel launched the influential Foreign Policy magazine with his friend Samuel P. Huntington, later the author of Clash of the Civilizations, and in conjunction with Carnegie Endowment for International Peace.