Also active in politics, Constantinou first raised money as part of the Tsongas campaign in 1991 but was recruited and later led the Bill Clinton Presidential finance committee/campaign in New Jersey and served as president of the New Jersey State Electoral College, one of 15 electors casting their votes for the Clinton/Gore ticket.

In the course of the 1997 Luxembourg European Union presidency, he led American delegations and participated in negotiations with EU officials on trade and global-cooperation issues.

In 2000 the School of Diplomacy was selected to serve as secretariat and project manager for the 2001 United Nations theme, Dialogue among Civilizations.

The year-long effort produced a report, published by the School, entitled Crossing the Divide and was presented by United Nations Secretary-General Kofi Annan to the General Assembly.

In 1999, Cyprus President Glafcos Clerides awarded Constantinou one of the Republic's highest distinctions, the Medal for Exceptional Services.