Prior to that, he held the rank of Ambassador as Deputy Permanent Representative at the U.S. Mission to the Organization of American States (OAS), leading a Mission in multilateral diplomacy efforts in support of U.S. bilateral policy from 2003-2006.

From 2000-2003 he served as Director of the State Department Political-Military Bureau (PM) Office of Regional Security and Arms Transfers, developing world-wide policy on sensitive, multi-million dollar arms transfers to key allies (including during operations in Afghanistan and Iraq). He dealt extensively with Congress for arms transfer approval, and with the private sector to strengthen U.S. defense industry.

He was Principal Officer of Consulate General Guayaquil, Ecuador, leading a 75-person, multi-agency team there from 1997-2000.

He served as State Department Political Advisor to two four-star Army General Commanders of U. S. Southern Command (then in Panama) from 1994-97.

Other overseas assignments include work as a Political Officer at U.S. Embassies in Buenos Aires, Argentina; Ottawa, Canada; Beijing, China; Bogota, Colombia; Georgetown, Guyana; and Santo Domingo, Dominican Republic.

From 1990-91, he worked on Capitol Hill as a Foreign Affairs Fellow with the American Political Science Association. He dealt mainly with issues of the House Appropriations Subcommittee on Foreign Operations.

During a leave of absence from the State Department, he was an attorney at a Los Angeles, CA law firm, specializing in corporate/international law and commercial litigation from 1982-1983.

Ambassador Dunn holds a Juris Doctor degree from Georgetown University Law Center, a B.S. in Foreign Service from Georgetown University; and has conducted non-degree study at the Johns Hopkins School of Advanced International Studies and the University of Fribourg (Switzerland).