[1][2] The regiment was mustered into service in the autumn of 1861 at Fort Schuyler in New York[3] when the government approved the commissioning of an Irish Brigade.

The men eventually settled on the number 88, in honor of the British Army's 88th Connaught Rangers, a unit composed of Irishmen, also where many of the now American troops received their training.

On December 15, 1862, the 88th received their specially made “Irish Colors” shortly after the Battle of Fredericksburg, Virginia.

The whole Irish Brigade was armed that day with M1842 .69 caliber smoothbore muskets loaded with buck and ball.

Again, the 88th New York and the Irish Brigade would storm a heavily fortified position, this time being the hills above Fredericksburg, VA, known as Marye's Heights.

At Gettysburg, the 88th fought with the rest of the Irish Brigade, at that time under the command of Patrick Kelly in John C. Caldwell's division of Winfield Scott Hancock's II Corps.

The 88th New York and the rest of the Irish Brigade took up position at the Wheatfield and held against several attacks from Confederate General James Longstreet's corps.