Hollister served as a delegate to the Republican National Conventions in 1940, 1944, 1948, and 1952. He headed the United Nations Relief Rehabilitation Association's mission to the Netherlands, 1945, and served as executive director of the Hoover Commission from October 1953 to July 1955. He was director of the International Cooperation Administration from June 15, 1955, until his resignation on September 13, 1957.