An official website of the United States Government Here's how you know

Official websites use .gov

A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS

A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Mark A. Sullo was named Deputy Assistant Secretary and Assistant Director of the U.S. Department of State’s Diplomatic Security Service (DSS) for Domestic Operations on June 1, 2021. In this role, he oversees all DSS programs within the United States, including operations at all field and resident offices, facility security, criminal investigations, counterintelligence, and protective operations.

As assistant director of the DSS Domestic Operations Directorate, Mr. Sullo serves concurrently as the chair of the International Security Event Group, a multi-agency body of more than 20 U.S. agencies—coordinating all U.S. security and law enforcement planning for major overseas events such as the Olympic Games.

“Domestically, DSS protects the secretary of state and high-ranking foreign dignitaries and officials visiting the United States, investigates passport and visa fraud, and conducts threat management, counterterrorism, and counterintelligence investigations,” Mr. Sullo said. “We also produce daily threat analyses focused on our overseas presence, train foreign law enforcement partners, and promote security cooperation between U.S. business and private sector interests worldwide.”

Mr. Sullo graduated from Western Kentucky University in 1994 with a bachelor of arts degree in mathematics. After graduation, he was commissioned as a second lieutenant in the Marine Corps and spent eight years on active duty before joining the Foreign Service in 2002 as a DSS special agent. He retired from the Marine Corps Reserve in 2015 as a lieutenant colonel.

His overseas postings include Iraq, Bahrain, and Kuwait. Domestically, he has served in the office of Mobile Security Deployments whose team members defend U.S. embassies and consulates in critical threat situations; on the protective detail for the U.S. ambassador to the United Nations; as the high-threat strategy coordinator for the State Department’s security training reforms following the 2012 attack on the U.S. consulate in Benghazi, Libya; and as the head of Protective Intelligence Investigations where he directed terrorism and threat investigations against the State Department and managed the DSS relationship with U.S. intelligence and counterterrorism communities to prevent bad actors who intend to cause harm from reaching U.S. soil.

Mr. Sullo most recently served as the Bureau of Diplomatic Security’s chief of staff. In that role, he demonstrated his expertise in counterterrorism, counterintelligence, investigations, and

protective security as he assisted in overseeing all law enforcement and security issues impacting the State Department on behalf of the assistant secretary of state for Diplomatic Security.

During a tour in 2014-2015, he served on the National Security Council staff. Mr. Sullo helped coordinate with U.S. federal agencies to prevent and respond to threats against all official and private American interests overseas on behalf of the Assistant to the President for Homeland Security and Counterterrorism, the National Security Advisor, and the President.

Mr. Sullo holds master’s degrees in security management from the George Washington University and in national security strategy from the National War College, in Washington, D.C., where he was one of 20 distinguished graduates out of a class of 208.

The Diplomatic Security Service (DSS) is the law enforcement and security arm of the U.S. Department of State. DSS has the largest global presence of any U.S. law enforcement organization, operating at more than 270 U.S. diplomatic posts in over 170 countries, and in 33 U.S. cities. The organization is responsible for investigating transnational crimes and for protecting State Department facilities, people, and information.

To learn more about the Diplomatic Security Service, please visit
For media queries, please contact

U.S. Department of State

The Lessons of 1989: Freedom and Our Future