He graduated from Harvard University and later joined the U.S. Foreign Service.

From 1978 to 1982, he worked in Bonn, Germany as a staff member for the FAS.

He served FAS positions in Lagos, Nigeria as Chief of the FAS office there from 1982 to 1986, and in Washington D.C. as Deputy Director of the Grains Division from 1986 to 1988, Deputy Assistant Administrator for International Statistics in 1988, Assistant Administrator for Export Credits/Acting General Sales Manager from 1988 to 1993, and as General Sales Manager for Export Credits from 1993 to 1999.

On July 7, 1999, Goldthwait was nominated by President Bill Clinton to be the United States Ambassador to Chad.

He was confirmed on October 10, 1999, and remained in that post until January 16, 2004, when he was succeeded by Marc M.