Mexican–American War
He served in the Mexican–American War as a first lieutenant in the 1st Mounted Rifles. Within a year, he was promoted to captain and cited for gallantry, being brevetted two grades to lieutenant colonel.[4] Porter spent the next fourteen years serving at various posts and forts on the frontier. He fought a duel in Texas with future Confederate general James J. Archer, whose second was Thomas J. Jackson, later "Stonewall" Jackson.
Civil War
Porter in 1862 Mathew Brady photo
On the outbreak of the Civil War he was serving as a colonel of the 16th U.S. Infantry. He was appointed as a brigadier general in May 1861, and commanded the 1st Brigade, 2nd Division at First Battle of Bull Run. He served as Provost Marshal of the District of Columbia, and was then appointed as Provost Marshal General of the Army of the Potomac in the Peninsula Campaign. In April 1864 he mustered out for health reasons.[5]
A photo of Porter by Mathew Brady circa 1862 survives.[6]