Garnett, Robert Selden was born on December 16, 1819 in Essex County, Virginia, United States. Son of Robert Selden and Olympia Charlotte (DeGouges) Garnett.
Graduated from the United States Military Academy, 1841.
Assistant instructor tactics United States Military Academy, 1843-1844. Aide-de-camp to General Wood, 1845. Brevetted captain in Battle of Monterey during Mexican War, 1846-1848.
Aide-de-camp to Zachary Taylor, 1846-1849. Commissioned First lieutenant with brevets of captain, major, 1850. Captain infantry, 1848-1850.
Commandant of cadets, instructor infantry tactics United States Military Academy, 1852-1854. Commissioned major, 1855. Commanded Puget Sound, also Yakima expeditions in N.W., 1856.
Commissioned brigadier general in command Confederate Army in N.W. Virginia, 1861. Served in Battle of Carricks Ford, Virginia, covered the retreat of his force from Laurel Hill across Cheat River in face of McClellan’s Army.