His books include:
* The Civil War: A Narrative (1988)
* The Black Experience in the Civil War: A Documentary History (1989)
* The Life and Times of Martin Luther King, Jr.: A Historical Reader (1991)
* The Struggle for Civil Rights (1993)
* The Life and Legacy of Rosa Parks (1995)
* The Civil War in the West: A Documentary History (1997)
* The Civil War in the East: A Documentary History (1999)
* The Civil War in the South: A Documentary History (2001)
Jennings has also written numerous articles and essays on the Civil War and the American Civil Rights Movement. His work has been published in journals such as The Journal of American History, The Civil War History, and The Journal of Negro History.
In addition to his writing, Jennings has also served as a consultant for several historical documentaries, including The Civil War (1990), The African-American Experience (1991), and The Civil Rights Movement (2003).
Jennings is a member of the Society of American Historians, the American Historical Association, and the American Civil War Society. He is also a recipient of the Lincoln Prize for Civil War Studies.