Her early assignments included tours as Consul General in Montreal, Canada; Deputy Chief of Mission at the U.S. Embassy in Managua, Nicaragua; and Economic Counselor in Paris, France and Port au Prince, Haiti.

She also served as the financial economist at the U.S. Embassy in Rome, Italy and at the U.S. Department of Treasury as well as desk officer for Guatemala.

She served as Senior Advisor for Counter Terrorism from 2004 to 2006, and as Deputy Assistant Secretary in the Bureau of International Narcotics and Law Enforcement.

The U.S. Air Force brought two Lockheed Martin F-22 Raptor tactical stealth fighter aircraft to Lithuania on April 27, 2015 for several hours.

McCarthy said that the visit of the U.S. Air Force jets demonstrated the American support of NATO and “commitment to Article 5 of the Washington treaty and collective defense".