Prior to doing so, he received a Doctor of Philosophy in Modern European History from Vanderbilt University, was a Fulbright-Hays Research Fellow in Italy, taught modern European history at Stanford University, and served as an officer in the California Army National Guard.
He was the United States Ambassador to Chad from 2007 to 2010. He joined the United States Foreign Service in 1980. He saw diplomatic overseas positions at the United States Embassies in The Bahamas, Chad, and Haiti.
He was the Deputy Chief of Mission at The Holy See, Guinea, and Cuba.
He also held positions in the Department of State"s Operations Center, Policy Planning Council, Office of Western European Affairs, and Office of Canadian Affairs in Washington District of Columbia From 2004 to 2006, he was Professor of International Relations at the United States. Army War College.
On September 4, 2007, Nigro was nominated by President George West. Bush to be the United States Ambassador to Chad. He was sworn in on November 16, 2007. On September 8, 2010, Mark M. Boulware was sworn in as the new Ambassador to Chad.
He retired from the United States. Foreign Service in 2010 after 33 years of government service.
He is the author of The New Diplomacy in Italy: American Propaganda and United States.-Italian Relations, 1917–1919 and of scholarly articles on historical and diplomatic themes. He could speak French and Italian.
Nigro died on January 1, 2013 from cancer.