Robert Patterson Hughes (April 11, 1839 – October 27, 1909) was an American military officer. He served from 1861 until 1903 and attained the rank of major general. A native of Canonsburg, Pennsylvania, he was educated at local academies and taught school before attending Jefferson College. He left college to join the Union Army for the American Civil War, and rose to the rank of colonel by brevet. After the war, Hughes received a commission in the United States Army. He participated in engagements of the American Indian Wars, and served for several years as aide-de-camp to his Alfred Terry, who became his brother-in-law.