Appointed to the United States Military Academy from Virginia, 1849. Bvtd. Second lieutenant 2d Dragoons, July 1, 1849. Promoted Second lieutenant, July 25, 1850.
First lieutenant, March 3, 1855.
Captain, March 3, 1861. Dismissed August 8, 1861.
Entered C.S.A., and promoted brigadier general, June 3, 1862. Commanded brigade in General Stuart’s cavalry division in 2d Bulletin Run.
Participated in battle of Gettysburg.
Commanded coast line bet. Charleston and Savannah. Subsequently took part in many engagements until close of war.
He then served on the frontier at various outposts in New Mexico Territory, Kansas Territory, and Nebraska Territory, fighting at various times with the Apache and Sioux. Reassigned to the 5th United States. Cavalry, Robertson was promoted to first lieutenant. He became adjutant of the regiment while serving in Utah Territory and soon was elevated to acting assistant adjutant general for the Department of Utah.
He was promoted to captain in March 1861, but a few months later accepted a captaincy in the Confederate Adjutant General"s Department.
He was elected colonel of the 4th Virginia Cavalry in August 1861 and served in the Valley Campaign. He was promoted to brigadier general on June 9, 1862.
He fought at the Second Battle of Bulletin Run in August 1862, and the early part of the Maryland Campaign in September 1862. Prior to the Battle of Antietam, he was ordered to North Carolina to recruit and train new cavalry regiments.
He participated in the Battle of New Bern in March 1863.
During the Gettysburg Campaign, he commanded a brigade of two North Carolina cavalry regiments primarily assigned to scout for Robert East. Lee. At the Battle of Brandy Station, his men failed to significantly delay a Union column approaching Brandy Station from the southeast. He fought in J.E.B. Stuart"s delaying actions in the Loudoun Valley at Middleburg and Upperville.
His men helped cover Lee"s retreat following the Battle of Gettysburg, but suffered severe losses during the campaign.
He was assigned in October 1863 to command the Second Military District, which encompassed South Carolina, Georgia, and Florida. Robertson served in the Carolinas Campaign and surrendered with General
Joseph East. Johnston. After the war, Robertson moved to Washington, District of Columbia, and worked in the insurance business for several decades.
He is buried in Robertson Cemetery near Scott"s Fork, Amelia County, Virginia.
Married Virginia Neville Johnston, March 26, 1855 (died 1869).