[1] Battery commander John Gibbon, soon to become a Major General, described Stewart as "the best first sergeant I ever saw in the service.".

At the Battle of Antietam, his artillery battery was the first deployed into the Cornfield, helping to stop Hood's Division.

[1] Stewart commanded the battery, the only regular artillery in the I Corps, during the Battle of Gettysburg.

[3] During the first day of fighting at Gettysburg, Stewart was placed west of the Thompson House, supported by the Sixth Wisconsin, plus the 11th and 143rd Pennsylvania regiments.

[4][5] On August 1, 1864, he was brevetted captain for "gallant services at the Battle of Spotsylvania Court House and during the present campaign before Richmond..."[6] After the war he remained in the Regular Army, being transferred to the 18th U.S. Infantry Regiment.