Brevetted Second lieutenant of engrs., 1842. Served as Second lieutenant on the fortifications of Hampton Roads, Virginia, 1843-1847. Assistant professor natural and experimental philosophy department engineering United States Military Academy.
Superintendent repairs at Fort Adams, Massachusetts, also in charge of various government surveys and improvements, 1847-1853. Promoted First lieutenant, 1853, resigned commission, 1854. Architect and civil engineer, Cincinnati.
President Coal River Navigation Company, Kanawha County, Virginia (now W. Virginia), 1856. Organizer Preston Coal Oil Corporation, manufacturers kerosene, 1857. Became volunteer aide-de-camp to General George B. McClellan in Ohio, 1861.
Made colonel, chief engineer Department of Ohio, United States.Army, 1861. Appointed colonel 23d Ohio Volunteer Infantry, 1861. Commissioned brigadier general United States Army, 1861.
Commanded brigade, won Battle of Rich Mountain, 1861. Succeeded McClellan as commanding general Department of Ohio, 1861. Chief new department of western Virginia, 1861, expelled Confederates, making formation of West Virginia possible.
Promoted major general United States Volunteers, 1862. Succeeded General John Pope in command Mississippi Army, involved in successful engagements at Iuka and Corinth, 1862. Commanded Army of the Cumberland.
Defeated at Battle of Chickamauga, 1863, relieved of command. Commanded Department of Missouri, 1864. Brevetted maj: general for services at Murfreesboro, 1865.
Resigned from United States Army, 1867. United States minister to Mexico, 1868, 69. Engaged in mining operations, Mexico, later California.
President Safety Powder Company, Los Angeles, California, 1875. Member United States House of Representatives from California, 47th-48th congresses, 1881-1885, Chairman of Commission on military affairs. Commissioned brigadier general on retired list United States.Army, 1889.
Register of the treasury, 1885-1893.