||He joined the staff of the Carnegie Corporation of New York in 1946, and in 1955 he became president of that group, and concurrently, the Carnegie Foundation for the Advancement of Teaching. He also served as an advisor to the U.S. delegation to the United Nations and as a consultant to the U.S. Air Force, which awarded him the Exceptional Service Award in 1956. He was a trustee of the Metropolitan Museum of Art and of the Educational Testing Service and a director of the Woodrow Wilson Foundation. He served as chairman of the Rockefeller Brothers Fund Panel on Education, and was chief draftsman of that group's widely circulated report, The Pursuit of Excellence.
He was also the founder of two influential national U.S. organizations: Common Cause and Independent Sector. He authored books on improving leadership in American society and other subjects. He was also the founder of two prestigious fellowship programs, The White House Fellowship and The John Gardner Fellowship at Stanford University and U.C. Berkeley. He received the Presidential Medal of Freedom in 1964. In 1966 Gardner was awarded the Public Welfare Medal from the National Academy of Sciences.