At the beginning of the American Civil War in 1861, Campbell chose to follow his home state and the Union cause.
He volunteered for service in the state forces on May 29, and was assigned as a captain of Battery A in the Pennsylvania Light Artillery.
On August 5 Campbell was promoted to lieutenant colonel in the Pennsylvania Artillery, and to colonel on September 13.
On December 20 Campbell participated in the Battle of Dranesville in Fairfax County, Virginia, and he resigned from the state forces on February 1, 1862.

Joining the Union Army in 1862, Campbell was appointed to command the 57th Pennsylvania Infantry as its colonel.
He led the 57th Infantry, part of Brig.
Gen. Philip Kearny's division, in the Peninsula Campaign of 1862, fighting at the Battle of Seven Pines on May 31.
In the battle Campbell's horse was shot from under him, and he was severely wounded three times.
Campbell was hit in the right arm, pelvis, and left leg, and was captured by Confederate soldiers.
Despite these injuries Campbell managed to escape later that day.

With his right arm still in a sling, Campbell led the 57th during the Fredericksburg Campaign in the winter of 1862.
At the Battle of Fredericksburg on December 13, he was again seriously wounded, hit in his abdomen and the same right arm.
The wound in his belly went through his liver, and Campbell was considered beyond hope and left for dead.
He had been appointed a brigadier general in the Union Army on November 29, 1862, but it was never confirmed and this appointment would expire on March 4, 1863.

Partially recovered, Campbell was promoted to brigadier general on March 13, 1863, and given command of the Union District of Wisconsin in the Department of the Northwest on November 7, 1864.
He led this district until the end of the war, and was mustered out of the volunteer service on January 15, 1866.
At the beginning of the American Civil War in 1861, Campbell chose to follow his home state and the Union cause. He volunteered for service in the state forces on May 29, and was assigned as a captain of Battery A in the Pennsylvania Light Artillery. On August 5 Campbell was promoted to lieutenant colonel in the Pennsylvania Artillery, and to colonel on September 13. On December 20 Campbell participated in the Battle of Dranesville in Fairfax County, Virginia, and he resigned from the state forces on February 1, 1862.
Joining the Union Army in 1862, Campbell was appointed to command the 57th Pennsylvania Infantry as its colonel. He led the 57th Infantry, part of Brig. Gen. Philip Kearny's division, in the Peninsula Campaign of 1862, fighting at the Battle of Seven Pines on May 31. In the battle Campbell's horse was shot from under him, and he was severely wounded three times. Campbell was hit in the right arm, pelvis, and left leg, and was captured by Confederate soldiers. Despite these injuries Campbell managed to escape later that day.
With his right arm still in a sling, Campbell led the 57th during the Fredericksburg Campaign in the winter of 1862. At the Battle of Fredericksburg on December 13, he was again seriously wounded, hit in his abdomen and the same right arm. The wound in his belly went through his liver, and Campbell was considered beyond hope and left for dead. He had been appointed a brigadier general in the Union Army on November 29, 1862, but it was never confirmed and this appointment would expire on March 4, 1863.
Partially recovered, Campbell was promoted to brigadier general on March 13, 1863, and given command of the Union District of Wisconsin in the Department of the Northwest on November 7, 1864. He led this district until the end of the war, and was mustered out of the volunteer service on January 15, 1866.
Charles Thomas Campbell