John A. Nagl is President of the Center for a New American Security (CNAS). He is also a member of the Defense Policy Board, a Visiting Professor in the War Studies Department at Kings College of London, and a member of the Council on Foreign Relations and the International Institute of Strategic Studies. Dr. Nagl is a member of the Joint Forces Quarterly Advisory Committee and of the Advisory Board of the Journal of the Royal United Services Institute.
With Nathaniel Fick, he suggested changes in the counterinsurgency doctrine used in Iraq for Afghanistan, based both on operational experience and the fundamental differences of the Iraqi and Afghan insurgencies. 
In September 2009, he observed that GEN Stanley McChrystal, the commander in Afghanistan, is showing a priority in protecting the population rather than holding land.  Nagl called this a "triage" decision, while Fick said it was important not to let al-Qaeda and the Taliban present a narrative that they had driven out the U.S.
While a military officer, he was in the team that wrote Field Manual 3-24: Counterinsurgency, the basis of current doctrine in Afghanistan and Iraq,  His last military assignment was as commander of the 1st Battalion, 34th Armor (1/34 Armor) at Fort Riley, Kansas, training Transition Teams that embed with Iraqi and Afghan units. He led a tank platoon in Operation Desert Storm and served as the operations officer of a tank battalion task force in Operation Iraqi Freedom. Nagl taught national security studies at the United States Military Academy Department of Social Sciences and in Georgetown University’s Security Studies Program. He served as a Military Assistant to two Deputy Secretaries of Defense and later worked as a Senior Fellow at the Center for a New American Security. He was awarded the Combat Action Badge by General James Mattis of the United States Marine Corps, under whose leadership he fought in Anbar Province in 2004.
- Ph.D., Oxford University, Rhodes Scholar
- Master of the Military Arts and Sciences Degree from the Command and General Staff College, where he received the George C. Marshall Award as the top graduate.
- Distinguished Graduate, United States Military Academy, 1988
- Nathaniel C. Fick, John Nagl (January/February 2009), "Counterinsurgency Field Manual: Afghanistan Edition", Foreign Policy (magazine)
- Jackie Northam (25 September 2009), "U.S. Troops Withdraw From Isolated Afghan Areas", NPR
- John Nagl, David Petraeus, James Amos, Sarah Sewall (December 2006), Field Manual 3-24: Counterinsurgency, US Department of the Army