Gardner received his country's highest award for bravery during combat, the Medal of Honor.

[1] Gardner's medal was won for being among the first to enter Fort Gregg during the Third Battle of Petersburg in Virginia on April 2, 1865.

[2] Gardner joined the Army from Egremont, Massachusetts in July 1862, and mustered out with his regiment in June 1865.

[1] The President of the United States of America, in the name of Congress, takes pleasure in presenting the Medal of Honor to Sergeant Robert J. Gardner, United States Army, for extraordinary heroism on 2 April 1865, while serving with Company K, 34th Massachusetts Infantry, in action at Petersburg, Virginia.

Sergeant Gardiner [sic] was among the first to enter Fort Gregg, clearing his way by using his musket on the heads of the enemy.