From September 2009 Ambassador Campbell has been the Ralph Bunche Senior Fellow for Africa Policy Studies, Council on Foreign Relations, New York. Ambassador Campbell writes articles and op-ed pieces, contributes chapters to larger studies and published a book titled Nigeria: Dancing on the Brink in 2010. The second edition was published in June 2013. His new book on South Africa, titled Morning in South Africa? has been accepted for publication. His case studies on Nigeria and South Africa were published in 2013 in a Council on Foreign Relations study of democratic transitions, Pathways to Freedom. Among his other publications is a Council on Foreign Relations Special Report, U.S. Policy to Counter Nigeris Boko Haram. He writes a daily blog, Africa in Transition and manages the Nigeria Security Tracker (http://on.cfr.org/ZUqR3h). He regularly makes scholarly presentations and serves on academic panels and conducts roundtables for Council members . He consults with the Department of State, the Department of Defense and agencies within the U.S. intelligence community. The British, Canadian, Danish, German, and Norwegian governments have also consulted him, as have private companies and non-governmental organizations. He regularly lectures in academic and government settings. He is on the board of the American University of Nigeria. In July 2018, Ambassador Campbell, along with Matthew Page, coauthored Nigeria: What Everyone Need to Know.

As the chief of mission in Nigeria from 2004 to 2007, Ambassador Campbell led one of the largest U.S. missions in Africa with the presence of many federal agencies. He participated in the formulation of policy and led in its implementation in the African country then of greatest strategic importance to the United States. He coordinated U.S. observation of the national elections in 2007. Following his retirement from the Foreign Service, Ambassador Campbell was a visiting professor at the University of Wisconsin-Madison for the 2007-2008 academic year. In 2008-2009, Ambassador Campbell returned temporarily to the Department of State to lead an Office of the Inspector Generas inspection of our diplomatic mission in Mexico and co-lead an inspection of our embassy in Iraq with a focus on management, leadership, and interagency coordination issues. Subsequently, he served briefly as interim Historian of the Department of State before moving to the Council on Foreign Relations in September 2009.

Ambassador Campbells previous domestic Department of State assignments included Deputy Assistant Secretary in the office of the Director General of the Foreign Service, Dean of the Department of Stats language training facility, Deputy Executive Secretary of the Department of State, and Director of the Office of UN Political Affairs in the Department. He has served at diplomatic missions in Lyon, Paris, Geneva, Lagos, Pretoria/Cape Town and Abuja. Before entering the U.S. Foreign Service he was a tenured Associate Professor of History, Mary Baldwin College, Staunton Virginia.