Marion A. Ross (October 9, 1832 – June 18, 1862) was a sergeant major of the United States Army who was awarded the Medal of Honor for gallantry during the American Civil War.

He was posthumously awarded the medal in September 1863 for actions performed during the Great Locomotive Chase in April 1862.

On 7 December 1861, after catching the attention of General Ormsby Mitchel, he was promoted to sergeant major and was assigned to the Secret Service, a group of 24 men led by Captain James J. Andrews, which met in Shelbyville, Tennessee.

His Medal of Honor citation reads:[2] The President of the United States of America, in the name of Congress, takes pride in presenting the Medal of Honor (Posthumously) to Sergeant Major Marion A. Ross, United States Army, for extraordinary heroism on April, 1862, while serving with Company G, 21st Ohio Infantry, in action during the Andrew's Raid in Georgia.

Sergeant Major Ross was one of 19 of 22 men (including two civilians) who, by direction of General Mitchell (or Buell), penetrated nearly 200 miles south into the enemy's territory and captured a railroad train at Big Shanty, Georgia, in an attempt to destroy the bridges and track between Chattanooga and Atlanta.