Stacie Pettyjohn is a Senior Fellow and Director of the Defense Program at CNAS. Her areas of expertise include defense strategy, posture, force planning, the defense budget, and wargaming.

Prior to joining CNAS, Pettyjohn spent over 10 years at the RAND Corporation as a political scientist. Between 2019–2021, she was the director of the strategy and doctrine program in Project Air Force. From 2014–2020, she served as the co-director of the Center for Gaming. In 2020, she was a volunteer on the Biden administration’s defense transition team. She has designed and led strategic and operational games that have assessed new operational concepts, tested the impacts of new technology, examined nuclear escalation and warfighting, and explored unclear phenomena, such as gray zone tactics and information warfare. Previously, she was a research fellow at the Brookings Institution, a peace scholar at the United States Institute of Peace, and a TAPIR fellow at the RAND Corporation.

Pettyjohn has authored or co-authored reports on a wide range of issues, including defense strategy and budgets, readiness and responsiveness, the role of airpower in defeating the Islamic State, competition with Russia, possible war fighting scenarios with North Korea, and command and control of multi-national NATO amphibious forces. Additionally, she has crafted a large body of work on the United States’ overseas posture, which explores the operational requirements, its vulnerability to attack, and the political access challenges that the United States faces.

Pettyjohn's work has appeared in The Washington Post, Foreign Affairs, War on the Rocks, Defense News, The National Interest, Foreign Policy, and Lawfare. She has a PhD and an MA in foreign affairs from the University of Virginia and a BA in history and political science from the Ohio State University.