With the exception of slight encounters at Thoroughfare Gap on the 20th, and at Haymarket on the 25th of June, the regiment did not again meet the enemy until it reached the battlefield of Gettysburg. On the morning of the 1st of July, the first day of the battle, it commenced the march from Uniontown, near the northern border of Maryland, where it had rested the previous night, and at dusk arrived on the field. At three o'clock on the morning of the 2d the brigade moved out to Cemetery Ridge, about midway between the Emmittsburg and Taneytown roads, and formed line of battle on the declivity, facing westward, with a slight stone wall in front, the Seventy-first on the right, the Fifty-ninth New York of the First Brigade on the left, the remainder of the brigade in rear under cover of the hill. In the rear of the Sixty-ninth, on the summit of the ridge, was posted Cushing's Battery of the Fourth United States.

During the forenoon there was only skirmishing in front, with some artillery firing. At two P. M. General Sickles advanced on the left, but was driven back beyond his first position. The enemy following up his advantage, advanced upon the position held by the Sixty-ninth, attacking with great fury. The Third Rhode Island Battery of Napoleon guns had been posted in front of the regiment, and as the enemy approached, poured in a heavy fire of canister, inflicting great slaughter. The battery was, however, compelled to yield before the enemy's advancing columns, and retired leaving one gun, of which the horses had been killed, being unable to take it away.

Reserving its fire until the enemy was within twenty yards, the regiment rose and poured in a deadly volley, which checked his advance. He soon rallied, and renewed his efforts to capture the piece in front, but was repulsed in every attempt with great slaughter, and was finally compelled to retire. The struggle here lasted nearly two hours. On the 3d skirmishing, with occasional artillery firing, was kept up through the entire morning. At about eleven o'clock all firing ceased and a death-like stillness prevailed. It was the stillness that precedes and presages the tornado; for at a little after noon a gun in front heralded the opening of an unparalleled fire of artillery. It was chiefly directed upon the left centre, where the brigade lay, and for two hours with unceasing fury the storm of shot and shell raged. The slight fence in front afforded little protection; for, being composed of small stones loosely thrown together, they were hurled with violence in all directions when struck by the powerful missiles of the guns.

As the fire of artillery ceased, a powerful body of infantry, three lines deep, carrying their pieces at a trail arms, and marching with the regularity of troops on parade, issued from the woods on the ridge opposite, and advanced across the open plain in front. The artillery in rear of the regiment, of which there were many pieces, poured in rapid rounds over the heads of the men; the infantry reserved their fire until he had approached within point blank range, when with a loud cheer they delivered a volley which checked and threw his front line into confusion. It was but for a moment, for rallying he again rushed forward.

Two of Cushing's guns had been brought close up to the wall, within the line of the regiment, and were worked with terrible effect, by the men of the Sixty-ninth and of the Seventy-first, the gunners having all been killed or wounded. But the shock of the enemy's onset was fearful, and the troops upon the right of the regiment were at length forced back, which uncovered its flank, and the order was given for two companies to swing back to the crest of the ridge for its protection. The enemy taking advantage of this opening, crossed the wall, and rushed on after, up to the little cluster of trees in the rear; but meeting so hot a fire, he returned to the wall and throwing himself upon the ground, gave token of surrender. But no power of the enemy could move the centre and left of the regiment, which clung to its position with unflinching tenacity, keeping up a deadly and unremitted fire, the men at times clubbing their muskets to beat back the foe, who seemed determined to cross the wall.

Broken and dispirited, many of their leaders fallen, the enemy at length gave up the contest, few of all that host, who had marched so defiantly forth, returning unscathed.. General Kemper fell in front of the regiment, and General Armistead just at its right. Many prisoners and battle-flags were taken. The loss in the regiment was very severe. It entered the engagement with two hundred and fifty-eight officers and men. Of these, six officers and thirty-six men were killed, seven officers and seventy-six men wounded, and two officers and sixteen men taken prisoners, an aggregate of one hundred and forty-three.

Colonel O'Kane, and Lieutenant Colonel Tschudy, brave men, who had served upon every battle-field where the regiment had stood, while at the head of their men cheering them on and applauding their determination to depend their native soil, were killed. Captains Michael Duffy and George C. Thompson, and Lieutenant Charles F. Kelly, equally brave and daring, were also among the killed. Lieutenant Colonel Tschudy had been wounded in the fight of the second day, but unwilling to leave the field, he resolutely kept the fore front, with his men, until, with his face to the foe, he was stricken down in death. Major Duffy who assumed command upon the fall of the Colonel and Lieutenant Colonel, which occurred early in the fight, was severely wounded while changing front at the critical moment in the battle, but stood by his men and directed the fight until the victory was won.

From Gettysburg the regiment, under command of Captain Davis, joining in pursuit of the rebel army, marched to a point on the Hagerstown and Sharpsburg Pike, where it came upon the enemy's lines, and was for two days employed in throwing up breast-works and in skirmishing. After the escape of Lee into Virginia, it moved with the army, and during the campaign which ensued, was employed at Banks' Ford early in September in guard and scout duty; in provost duty at Culpepper; in reconnoitering at Somerville Ford, on the Rapidan; in reducing fortifications upon the Rappahannock, near Rappahannock Station; in guarding the wagon train on the retreat to Centreville, in which it was frequently attacked by irregular parties coming in upon its flank; in the rifle-pits at Bull Run on the occasion of Meade's second advance, where the artillery was warmly engaged; at Robertson's Tavern in the preliminary operations to the movement upon Mine Run, losing one killed and six wounded; and finally at Mine Run with the brigade, where it was held in readiness to lead the storming party in the grand assault upon the enemy's works, but was relieved without coming to action on the abandonment of offensive operations.

Winter-quarters were established at Stevensburg, and on the 14th of March, 1864, a sufficient number having re-enlisted to secure the continuance of the organization, they were given a veteran furlough, and returned to Philadelphia. While here the green flag which had been carried with the national colors in all its campaigns, was deposited in Independence Hall and a new one was presented by its friends. Upon the resignation of Major Duffy on account of wounds, Captain Davis was promoted to succeed him, and took command of the regiment. General Webb now held command of the brigade, General Gibbon of the division, and General Hancock of the corps.