Abner was a musician in Company E of the 13th Pennsylvania Infantry Volunteers for three months in 1861. He was recruited in Pittsburgh and mustered in on April 25 at Camp Curtin, Harrisburg by Captain Seneca G. Simmons. The regiment was in the 4th Brigade, 1stDivision. The regiment trained at Camp Scott, near York, for six weeks. He was mustered out at Pittsburgh on August 6.
On August 7, 1862, Abner enrolled in Company C of the 155th Pennsylvania Infantry Volunteers in Pittsburgh for the duration of the war. He was mustered in on August 22 at Pittsburgh. The regiment was mustered in at Camp Howell, Pittsburgh, on September 2, 1862. Abner served as a private.
At first, the 155th Regiment was in the Second Brigade, Third Division, Fifth Corps. Sometime between May 3 and July 1, 1863, the regiment was switched to the Third Brigade, Second Division. As of the spring of 1864, it was in the First Division. The regiment fought in Pennsylvania, Maryland and Virginia.
The 155th Regiment Pennsylvania Infantry was held in reserve during the battle of Antietam on September 17, 1862. The regiment's first battle was on December 13, 1862, at Fredericksburg, Virginia. Abner Adams may have been wounded in that battle. On December 17, 1862, he was sent to a hospital in Providence Grove, Rhode Island. The reason for his hospitalization was not documented in his military records. He returned to his company sometime between July 17 and September 1, 1963, probably in late July.
Abner was killed in action at the Battle of the Wilderness on May 5, 1864. He and Private Marion Hartley met their fate on the skirmish line on opening the battle. Their bodies were never recovered from the enemy. His body is probably buried in the Fredericksburg National Cemetery. Abner was posthumously mustered out in the field on June 2, 1865.