Robert was born on the 7th of June, 1841 in Centre County, Pennsylvania, and he joined the 148th Pennsylvania Infantry in Milesburg in August of 1862. It was his actions during the Battle of Spotsylvania Court House that would earn him the Medal of Honor. The citation reads:

The President of the United States of America, in the name of Congress, takes pleasure in presenting the Medal of Honor to Private Robert Wesley Ammerman, United States Army, for extraordinary heroism on 12 May 1864, while serving with Company B, 148th Pennsylvania Infantry, in action at Spotsylvania, Virginia, for capture of battle flag of 8th North Carolina (Confederate States of America), being one of the foremost in the assault.

During this battle, Robert lost his right leg which led to his discharge in May of 1865. Robert Wesley Ammerman died on the 30th of September, 1907 at the age of 66 and is buried in the Lost Creek Presbyterian Cemetery in McAlisterville, Pennsylvania.