In August 2023, Mary Ellen Callahan began as Assistant Secretary for the Department of Homeland Security’s (DHS) Countering Weapons of Mass Destruction Office (CWMD). CWMD leads the Department’s efforts and coordinates with domestic and Iinternational partners to safeguard the United States against chemical, biological, radiological, and nuclear (CBRN) threats.

Ms. Callahan previously served as Chief of Staff to the Deputy Secretary of DHS, John K. Tien (and briefly for Acting Deputy Secretary Kristie Canegallo), from September 2021 through August 2023. She provided substantive policy advice to the Deputy Secretary on a wide range of domestic and international policy issues and managed the day-to-day operations of the office with specific foci on DHS operating budget, human capital actions, and facilities management.

As Chief of Staff to the Deputy Secretary, Ms. Callahan was a key interlocutor and partner to Departments, Agencies, Office leaders, interagency partners, and the White House. Her stewardship of the Department’s vital national security interests was critical to gains made in the National Operations Center, operations to counter-human smuggling, international multi-lateral relationships, and continuity of operations and government, including resilience.

Ms. Callahan also previously served in the Department as the Chief Privacy Officer and Chief FOIA Officer under Secretary Janet Napolitano from March 2009 through August 2012. She oversaw the systemization of privacy protections through the lifecycle of Department initiatives. She represented DHS in extensive outreach and negotiations with counterparts in the European Union, Canada, and other countries to explain the U.S. privacy framework, and to negotiate multi- lateral information sharing agreements that complied with privacy laws.

In addition to her federal experience, she served as Assistant General Counsel for Privacy and Cybersecurity at The Walt Disney Company from 2017 through 2021. She was the lead counsel on COVID- 19 corporate responses, including Return-to-Work, COVID testing and data storage for studio and TV productions, and implementing vaccine requirements. She was a partner at two major international law firms, serving as the Founder and Chair of Jenner & Block’s Privacy and Information Governance Practice from 2012 to 2017, and Co-Chair of the Privacy Working Group at Hogan & Hartson (now Hogan Lovells) from 2005 to 2009.

Ms. Callahan has received multiple professional awards and recognition, including receiving the DHS Outstanding Service Medal from Secretary Mayorkas in August 2023 at the end of her tenure as Chief of Staff to the Deputy Secretary.

Ms. Callahan is a graduate of the University of Pittsburgh, where she was on the Board of Trustees from 2009 to 2022, and The University of Chicago Law School. She is a Truman Scholar (Pennsylvania, 1988).