With the outbreak of World War II, Brookings researchers aided the administration with a series of studies on mobilization. More than one year before Pearl Harbor, Charles O. Hardy's Wartime Control of Prices was prepared at the request of the War Department. Studies of manpower needs helped Congress balance the requirements of the armed services with the demand for civilian labor in a war economy. Brookings resident staff shrank as scholars went into service with the military or other wartime agencies. The two research divisions were consolidated and the programs of the training division were suspended.

With the end of the war, Brookings researchers turned their attention to postwar problems. As the nation assumed a more active role as a world power, Leo Pasvolsky established an International Studies Group, with the goal of analyzing U.S. foreign policy and training specialists in international affairs. In 1948, Brookings was asked to submit a plan for the administration of the European Recovery Program. The resulting organization scheme assured that the Marshall Plan was run carefully and on a businesslike basis.