At Gettysburg, O'Rorke was back in command of his regiment while Brig. Gen. Stephen H. Weed commanded the 3rd Brigade. The 140th New York arrived in time for the second day of fighting (July 2, 1863). Brig. Gen. Gouverneur K. Warren was desperately searching for units to defend Little Round Top, and he encountered O'Rorke's New Yorkers, the rearmost regiment in Weed's brigade, on their way to reinforce the III Corps. O'Rorke initially declined Warren's request for assistance because he was under orders to follow his brigade. Warren told him, "Never mind that, Paddy. Bring them up on the double-quick and don't stop for aligning. I'll take the responsibility." O'Rorke rushed his men to the crest of the hill and plunged down its western face without pause, driving the attacking Confederates back down the slope. During the counterattack, O'Rorke caught up his regimental colors and, mounting a rock to urge on his men, was struck in the neck and fell dead. The Comte de Paris in his "Histoire de la guerre civile en Amérique" (VI, iv, 379) says this was one of the most striking and dramatic episodes of the battle. A decorated member of O'Rorke's command, Lieutenant Porter Farley, in his noted work "An Unvarnished Tale: The Public and Private Civil War Writings of Porter Farley", described O'Rorke's action on Little Round Top as among the most instrumental of the entire civil war, and many respected military historians have further commented that O'Rorke's service, heroism and selflessness, at such critical time in the battle, were at least equal to that of the much better known, Congressional Medal of Honor recipient, Joshua Lawrence Chamberlain.