Gallagher in 2024 was the John L. Nau III Professor in the History of the American Civil War at the University of Virginia.

He then did graduate study in history at the University of Texas at Austin, receiving a Master of Arts in 1977 and a Ph.D. in 1982.

He is the presenter of an Audible series of lectures entitled The American Civil War.

These are currently available on Audible as a series of read lectures which go into great detail on the Civil War.

In 2021, Gallagher received The Lincoln Forum's Richard Nelson Current Award of Achievement.