He had long been active in the militia, and was appointed a brigadier general in 1855. During the American Civil War he became colonel of the 136th New York Volunteer Infantry, and commanded it at the battles of Chancellorsville, Gettysburg, Lookout Mountain, Missionary Ridge, Resaca, Dallas, Atlanta, Sherman's March to the Sea and Bentonville. He was brevetted a major general of volunteers. Afterwards, he resumed the practice of law at Geneseo.