He was commissioned as an officer through the University of Pennsylvania's Army ROTC program, which he initially joined as a means of financing his education there.

"[5] While still on active duty, but "laid up with a non-combat knee injury," Exum wrote his first book, This Man's Army: A Soldier's Story from the Front Lines of the War on Terrorism.

This blog, "dedicated to following issues related to contemporary insurgencies," was followed by many notable students and practitioners of counterinsurgency in the military, academia, and the media.

[citation needed] He served as Deputy Assistant Secretary of Defense for Middle East Policy in the US Government from 2015 to 2016.

In particular, he is critical of the U.S. government's reliance on private military corporations in Iraq and Afghanistan as well as what he sees as the misuse of drones in eliminating terror targets.