The U.S. Mission to the International Atomic Energy Agency (IAEA) was established in September 1957, with the appointment of Ambassador Robert Moody McKinney as the first Permanent Representative. From 1957 through 1999, the Permanent Representative of the USA to the IAEA was not resident in Vienna, Austria but was based in Washington, D.C.

In order to have a physical presence in the absence of the Permanent Representative, in September 1961, a Resident Representative of the USA to the IAEA was assigned as Principal Officer for the U.S. Mission to the IAEA. This position did not come with an Ambassadorial rank until 1970.

Amid all these changes, in 1968, another U.S. Mission was opened – the U.S. Mission to the United Nations Industrial Development Organization (UNIDO).  This U.S. Mission, with its focus on only one UN Organization, was headed by a Principal Officer. The position of Principal Officer to UNIDO was eliminated in 1977 although the Mission remained until 1997, when the U.S. withdrew from UNIDO.

In May 1983, the U.S. Mission to UNIDO and the U.S. Mission to the IAEA were merged into the U.S. Mission to International Organizations in Vienna, under the leadership of a resident Ambassador and Permanent Representative.