He then attended the University of Geneva and the Graduate Institute of International Studies, and received a doctorate in political science in 1935.
From 1947 through 1951, he was the first chief of staff of the United States Senate Committee on Foreign Relations.
During this time, the Committee oversaw the United States' involvement in the creation of NATO and the Marshall Plan.
In 1955, President of the United States Dwight D. Eisenhower nominated Wilcox as Assistant Secretary of State for International Organization Affairs and, after Senate confirmation, Wilcox served in this office from September 6, 1955, through January 20, 1961.
Leaving government service in 1961, Wilcox became dean of the Johns Hopkins University's School of Advanced International Studies.