Robert Patterson was born on January 12, 1792, in City Tyrone, Ireland. He and his father, who was banished from Ireland for insurrection, immigrated to the United States in 1798. As a young man, Patterson went into the banking business in Philadelphia, Pennsylvania. He fought in the War of 1812, and left the military in June of 1815 in order to begin a wholesale business in Pennsylvania. A Jacksonian Democrat, he became influential in Pennsylvania politics, and extended his business interests to the West and South.
Patterson fought in the Mexican War, as a major general of volunteers, and served on Gen. Winfield Scott's staff. Patterson returned to business until the Civil War, obtaining a sugar plantation in Louisiana and 30 cotton mills in Pennsylvania. When the Civil War began, General Scott mustered him into the Union volunteer service. Commissioned major general of Pennsylvania volunteers, he was placed in command of the Department of Pennsylvania.
In May of 1861, Patterson responded timidly and poorly to instructions from Scott to retake the US arsenal at Harpers Ferry. His failure to act effectively gave Confederates the opportunity to evacuate the arsenal, destroy the buildings and join the main Confederate army at Manassas. Scott ordered Patterson to be relieved of command. Patterson received an honorable discharge on July 27, 1861, only three months after he was commissioned.
After the Civil War, he wrote a booklet, "A Narrative of the Campaign in the Valley of the Shenandoah in 1861," (1865), and worked on his business interests. Patterson died in Philadelphia, Pennsylvania, on August 7, 1881.