Maresca was chef de cabinet for two secretaries general of NATO, Manlio Brosio and Joseph Luns, in Brussels.

In this role, Maresca was responsible for helping to create the so-called Minsk Group, which since 1992 has been the basic forum for negotiation of a peaceful settlement of the N-K conflict.

He helped to establish the principle that the newly independent states from the former USSR were entitled to membership in the OSCE, thus giving them their first direct link with Europe and North America.

From 1997–99, Maresca served as vice president for international relations, Union Oil of California (Unocal), where he created a single, company-wide corporate social responsibility program which directed millions of dollars toward constructive charitable objectives to countries in need.

Headquartered in Costa Rica, the United Nations-mandated University for Peace was established in December 1980 as a Treaty Organization by the UN General Assembly.

Maresca has served and currently serves on a number of boards including the American University of Paris; International Research and Exchanges Board (IREX); Search for Common Ground; National Bureau of Asian Research (NBR); Women and Public Policy Program, Kennedy School, Harvard University; Humanitarian Affairs Review; Commission for Security and Cooperation in the Persian Gulf; American-Iranian Council (AIC); Geneva Centre for Democratic Control of the Armed Forces (DCAF); AIG Silk Road Fund; ISO Senior Advisory Group on Corporate Responsibility; Commission on Business in Society of the International Chamber of Commerce (ICC); OECD Secretary General's Round Table on Corporate Social Responsibility.