The corps was assembled by Burnside at Newport News, Virginia, from his two brigades from North Carolina and Isaac Stevens's division from Hilton Head.

He obtained permission for the transfer of his old corps to this field of operations, and on March 19, 1863, General Parke was ordered to proceed there with his two remaining divisions, Willcox's and Sturgis's.

In June it was ordered to the support of Ulysses S. Grant, who was then besieging Vicksburg, and proceeding there promptly, it participated in the investment of the city, although not under fire.

Upon the surrender of Vicksburg, Parke's two divisions joined the main army in its movement on Jackson, Mississippi, and became engaged in the fighting there, with a loss of 34 killed, 229 wounded, and 28 missing; total, 291.

The corps left Mississippi in August, 1863, and returned to Kentucky, where, after a short rest, it joined in Burnside's advance into East Tennessee, a movement that had already commenced.

Ferrero's Division had a sharp little fight at Blue Springs, Tennessee, October 10, 1863, and the whole corps was engaged, November 16, at Campbell's Station.

This was followed by the occupation of Knoxville and the gallant defense against James Longstreet's besieging forces, terminating December 4, in the defeat and withdrawal of the enemy.

Ferrero's Colored Division had never been under fire, while many of the white regiments in the corps were newly organized, or had served previously on garrison duty only.

His command in Northern Virginia consisted of the Army of the Potomac, under Maj. Gen. George G. Meade, and the IX Corps operating separately, reporting directly to Grant.

By the time of the Battle of North Anna, however, Grant acknowledged that this arrangement was ineffective and he convinced Burnside, along with General Parke, his chief of staff, to waive the question of their superiority of rank over Meade.

On June 19, Ferrero's (4th) Division of black troops rejoined the corps, having been absent during the whole of the previous campaign, engaged on duty at the rear.

The part of the line occupied by the IX Corps was very near the enemy's works, and an incessant firing was kept up during the siege, resulting in a daily loss of men, killed or wounded.

The IX Corps was prominently connected with the siege because of its role in the infamous Battle of the Crater, in which a lengthy mine shaft was dug from its line to under the Confederate works.

This mine, which was excavated by the coal miners of 48th Pennsylvania, Potter's Division, was successfully exploded with four tons of gunpowder, resulting in an enormous crater, but the assault that followed was a failure.

At the battle of the Weldon Railroad, August 19–21, 1864, the three divisions of White, Potter, and Willcox were engaged with considerable loss, although the three combined numbered less than 6,000 muskets; casualties were 60 killed and 315 wounded.

But in December, Ferrero's Division was permanently detached, and most of his regiments were transferred to the newly organized XXV Corps, which was composed entirely of black troops.

This division rendered gallant service at Fort Stedman, and Hartranft added to his laurels by the ability displayed at that critical juncture.

The morning report for March 31, 1865, showed a corps strength of 18,153, "present for duty, equipped," and 36 pieces of light artillery.

With this force the IX Corps entered upon the final campaign, taking a prominent part in the storming of Petersburg, April 2, 1865, which resulted in the evacuation of Richmond and the downfall of the Confederacy.