Callahan joined the Foreign Service in 1979 and, after training and language classes, served in Costa Rica as assistant cultural affairs officer and in Honduras, first as cultural attaché and later as press officer. In 1985 he was assigned to the embassy in London as the ambassador’s speechwriter and assistant press attaché. In 1989 he returned to Latin America as counselor for public affairs in La Paz, Bolivia. 

 

After a tour in Washington from 1992-1995, which included Greek language training, Callahan became the counselor for public affairs in Athens and then from 1998-2002 he served as minister counselor for public affairs in Rome.  That summer he returned to the United States, where he taught for two years at the National War College in Washington, DC, on a detail assignment from the State Department.  In 2004, he volunteered to serve for one year as embassy spokesman and press attaché in Baghdad. 

 

He then served as director of public affairs at the Office of the Director of National Intelligence in Washington, DC, followed by his assignment as the first public diplomacy fellow at the School of Media and Public Affairs at George Washington University, a position created in August of 2005.