George Stoneman was born in Busti, New York on August 22, 1822, the first of ten children. He graduated from the U.S. Military Academy at West Point in 1846, where he had been the roommate of future Confederate general, Thomas "Stonewall" Jackson. From 1846 to 1861, most of his service was in the west, particularly California and Texas. In 1861, he was a captain in the 2nd US Cavalry, stationed at Fort Brown, Texas.
He returned east and became a major in the 1st US Cavalry. On August 13, 1861, he was promoted to brigadier general and made chief of cavalry for the Army of the Potomac. In the summer of 1862, he switched to infantry and was placed in command of the III Corps. He was promoted to major general of volunteers in November 1862, but following the Battle of Fredericksburg the next month, he returned to the Cavalry Corps. Gen. Joseph Hooker blamed Stoneman and the cavalry for the Union defeat at the Battle of Chancellorsville in May 1863, and Stoneman was relieved of his command. After medical treatment for a chronic condition in Washington, D.C., he became Chief of the U.S. Cavalry Bureau, a job he hated because it was a desk job.
In 1864, Stoneman assumed command of the Cavalry Corps for the Army of the Ohio and, during the Atlanta Campaign that summer, he was captured by the Confederates at Macon, Georgia. He was the highest ranking Union prisoner of the entire war, but was only held for three months before being exchanged. From March 28 through April 26, 1865, Stoneman led a very successful raid through western North Carolina. Among his primary targets were the towns of Winston, Salem, High Point, and Salisbury. His main objective was accomplished when he freed Union captives from the Confederate prison at Salisbury. For his gallantry, he was promoted to brevet major general in the regular army.
Stoneman was appointed commander of the Department of Tennessee in June 1865 and administered the early Reconstruction government at Memphis. Not finding Reconstruction politics to his liking, he reverted to his previous rank of lieutenant colonel in the regular army and, in September 1866, he took command of the Department of Arizona. His handling of Indian affairs caused controversy, and he was relieved of his command in May 1871.
Stoneman moved his wife, Mary, and their four children to California, where they lived on a 400-acre estate. He served as a state railroad commissioner from 1876 to 1878 and served one term as governor of California from 1883 to 1887. He returned to Buffalo, New York in need of medical treatment and financially broke after a fire destroyed his home. He died of a stroke on April 12, 1894. His former estate is now a state historical landmark in California, and numerous schools, streets, and other landmarks are named for him.