Natives of County Cavan, Ireland, the O'Rorke family emigrated to Rochester, New York when Patrick was between the ages of two and four. After completing an education in the city's public schools, he was appointed to the US Military Academy at West Point, from which he graduated first in his class (Second Class of 1861) and subsequently accepted a commission in the Engineers.
O'Rorke was assigned to duty on the staff of Brigadier General Daniel Tyler. He saw action at the First Battle of Bull Run where a horse was killed under him and a bullet passed through his coat. Following Bull Run, O'Rorke took up engineering duties in the defenses of Washington. During the Fall of 1861, O'Rorke found himself assigned to the engineering staff of the Port Royal Expedition. In March of 1862, he was breveted to Captain. In September of the same year, bored with the slow paced duties of an engineering officer, he accepted command of the 140th New York Volunteer Infantry. Patrick O'Rorke was 26 years old.
At Gettysburg, O'Rorke sacrificed himself and his men to save the Union right on Little Round Top. Summoned to Little Round Top by Gouverneur K. Warren and seeing that the 4th and 5th Texas were breaking through the right flank of the 16th Michigan, O'Rorke threw his men into the breech. O'Rorke was killed in one of the first volleys. A bullet cut through his neck, ending a promising carrer; but, the men he had trained were able to secure the flank and very possibly the battle.
For further information see also The Supreme Event in its Existence, The 140th New York on Little Round Top and Addendum. Also, The Beau Ideal of a Soldier and a Gentleman: The Life of Col. Patrick Henry O'Rorke From Ireland to Gettysburg. All written by Brian A. Bennett.