The regiment was attached to the IX Corps of the Army of the Potomac and took part in Lieutenant General Ulysses S. Grant's Overland Campaign in the spring of 1864.

The regiment departed Massachusetts on March 20 for Annapolis, Maryland where Major General Ambrose Burnside was reorganizing his IX Corps for the spring campaign.

The regiment bivouacked there for three days before the Army of the Potomac crossed the Rapidan River and the Overland Campaign commenced.

The 56th Massachusetts was attacked on their left flank and within minutes of the start of their engagement, Col. Charles Griswold was shot in the neck and killed.

[1] As Grant ordered a movement by the left flank in an effort to outflank Lee's army, the IX Corps (including the 56th Massachusetts) marched the widest arc, first moving east towards Fredericksburg, Virginia and then southward on May 8 and 9 towards the crossroads known as Spotsylvania Court House.

While they executed this wide march, other elements of the Army of the Potomac engaged the Confederates and both forces began to dig in.

The 56th Massachusetts was not engaged until the IX Corps advanced along the Fredericksburg Pike on May 12 and assaulted the Confederate left flank.

[1] The 56th Massachusetts was initially held in reserve during this assault but later in the day made an effort to carry the enemy's breastworks by direct charge.

[4] Due to casualties among senior officers, the colonel of the 56th Massachusetts, Stephen Weld, was temporarily advanced to brigade command and performed ably during the assault on May 12.

[5] After several days of digging rifle pits, making breastworks and exchanging light fire with enemy skirmishers, the 56th Massachusetts took part in another assault on the Confederate works surrounding Spotsylvania Court House on May 18.

[4] The 56th Massachusetts marched for three days with their brigade after Grant decided to disengage at Spotsylvania Court House and again attempted to move around Lee's flank.

When their brigade reached open fields on the south side of the North Anna River, they deployed in lines of battle.

The 56th Massachusetts was one of the regiments assigned to support the 2nd Maine Battery and were forced to lie prone in front of the guns.

Prior to the June 17 assault, the regiment numbered only 130 men in contrast to the roughly 1,000 that had left Boston in March.

In the days leading up to the June 17 assault on the Confederate entrenchments around Petersburg, Virginia, the 56th Massachusetts endured long marches as Generals Grant and Meade arrayed their troops for an offensive.

A division of African-American troops prepared a plan of attack and trained to lead the main assault after mine was exploded.

However, the day before the attack, Gen. Meade changed the plan, instead assigning Gen. Ledlie's division (including the 56th Massachusetts) to lead the assault.

In the late afternoon, troops under Confederate Maj. Gen. Henry Heth mounted a sweeping counterattack which took IX Corps division under Brig.

[4] The 56th Massachusetts spent the winter of 1864–1865 at Fort Alexander Hays, a fortification near the left flank of the Petersburg siege lines.

They remained there conducting picket duty without much incident until the general Union assault on the Petersburg lines which took place on April 1 and 2, 1865.

After Lee's surrender, the 56th Massachusetts was ordered to march for City Point, Virginia—a distance of some 60 miles which they completed in three days.