Primarily a staff officer and operations planner until the latter stages of the war, he commanded an infantry brigade in the Western Theater in 1864 and 1865.

Through the influences of his powerful father, he received a promotion to lieutenant colonel and a new position as a staff officer and aide-de-camp to Union Maj. Gen. David Hunter.

[1] He was involved in planning the Union operations against the Confederate defenses of Charleston, South Carolina, but missed participating in the major attacks while recovering in Washington, D.C., from a riding accident suffered in the field.

[2] In August 1864, he finally received his long desired promotion to brigadier general, but did not get a field command initially as his sponsor Hooker had since left the army.

James Fessenden arrived in Virginia and assumed command of a brigade in the XIX Corps under Maj. Gen. William H. Emory.

He participated in the Battle of Cedar Creek in October, engaged in scouting duty, and then was assigned command of the Union garrison in the defenses of Winchester, Virginia, in January 1865.

He subsequently commanded troops under Maj. Gen. Winfield S. Hancock and an occupation garrison in South Carolina before mustering out of the army on January 15, 1866.