A career Foreign Service Officer, William Brownfield was United States Ambassador to Colombia.

On August 3, 2010, the United States confirmed Peter Michael McKinley as the new ambassador to Colombia.

His other overseas postings include service as Counselor for Humanitarian Affairs in Geneva, and assignments in Argentina and El Salvador.

In Washington, Ambassador Brownfield's assignments have included Deputy Assistant Secretary of State for Western Hemisphere (WHA), Director for Policy in the Bureau of International Narcotics and Law Enforcement Affairs, Executive Assistant in the Bureau of Inter-American Affairs, Member of the Secretary's Policy Planning Staff, and Special Assistant to the Under Secretary for Political Affairs.

[3] Starting on January 10, 2011, Brownfield served as Assistant Secretary of State for the Bureau of International Narcotics and Law Enforcement Affairs.