When Jean Monnet came to Washington in 1940, he met up with many of the key figures in the "inner circle" surrounding President Roosevelt of which Averell Harriman was a member. In his position as Secretary of Commerce he had strongly backed Monnet in his plans for Europe. As early as June 1950, Harriman had given Monnet the impression that loans would be made available if the Schuman Plan came into being. Harriman, because of his significant contribution to the Marshall Plan was appointed as US special representative in Europe, where he saw the Schuman Plan unfold and the establishment of the ECSC. He wrote to Dean Acheson, that he felt it was a big step toward peace in Europe. Therefore, Harriman was an enthusiastic and influential supporter of US co-operation in European Unity designs in his post in Europe and in his later position as special presidential adviser to Truman on foreign affairs. In September 1931 the Atlantic Council decided to establish a Temporary Council Committee (TCC) with the task of establishing NATO military needs with reference to the economic position of its member states. Harriman was chosen as chairman and US representative and Monnet, on the advice of Robert Schuman accepted the position of French representative. On becoming President, Kennedy an admirer of Monnet, was determined to continue US support for European integration, so he appointed officials with a background in dealing with Europe to key foreign office positions. Harriman, who initially became the assistant Secretary of State for Far Eastern affairs, with responsibility for China, Korea and Formosa in 1961, became under-Secretary of State for political affairs in 1963. In this position he was a key figure in the signing of the Declaration of Atlantic Unity endorsed by the NATO Parliamentarians Conference, November 1962.

The originals are held in various Archives and Presidential Libraries in the USA