The Confederacy of Southern states broke from the Union and took an aggressive stance by firing on Fort Sumter in early April 1863. Days later, Lincoln called for men to volunteer their military service to the Union cause. And by late April, 1863, Tourgee left the University of Rochester to enlist with the 27th New York Volunteer Infantry. According to various records, Tourgee fought at the first Battle of Bull Run at Manassas, where he suffered a debilitating spinal injury that would plague him for the remainder of his life. During the battle, 130 men from the unit were brutally killed, and many more wounded, which must have made quite an impression on the young student scholar-turned soldier.
Tourgee returned home to Ohio to recuperate. During this time, he took up the study of law with a local firm (he received his license to practice in 1864, #595), but with the war still raging, Tourgee once again enlisted with the Union Army, this time as a first lieutenant with Company G of the newly formed 105th Ohio Volunteers Infantry. Tourgee was again wounded and this time captured and held in a Confederate prison until he was exchanged in May 1863.