See his autobiography (1961).
Shotwell attended the Paris Peace Conference as a member of "The Inquiry" - President Woodrow Wilson's foreign policy advisory group. After the war he worked tirelessly to counter US isolationism and to promote US entry into the League of Nations. Shotwell met with the French Minister of Foreign Affairs Aristide Briand in Paris and suggested that a bilateral treaty be negotiated that would outlaw war between the U.S. and France. Their work led to the Kellogg-Briand Pact being signed on August 27, 1928.
In 1937, he was appointed Bryce Professor of the History of International Relations at Columbia University. He served as the Director of Economics and History (1942-49) then president of the Carnegie Endowment for International Peace (1949-50). He attended the 1945 San Francisco Conference that drafted the Charter of the United Nations as a private consultant to the U.S. State Department.
In addition to his many books, Shotwell was also co-author of several authoritative studies on international relations and was the editor of a series of 150 volumes of the Social and Economic History of the World War as well as a series of twenty-five studies on Canadian-American relations, both sponsored by the Carnegie Endowment for International Peace. He also contributed nearly 250 articles to the 11th edition of the Encyclopaedia Britannica.
The "James T. Shotwell Professor of International Relations" at Columbia University was named in his honor.
Shotwell was married to Margaret Harvey and had two daughters, Helen and Margaret Grace. He maintained a home in Woodstock, New York and was instrumental in getting American artist Anita Miller Smith to become a writer and to publish the service record of all Woodstock people who had fought in the war as part of Smith's 1959 book on the town's official history.