On the outbreak of the Civil War, he enlisted as a private in Company H of the 2nd Ohio Infantry Regiment on April 17, 1861, for three months of service, during which time he participated in the First Battle of Bull Run.

He soon re-enlisted in the Army for a three-year term, being mustered in on September 11, 1861, at Camp Dennison, Ohio, and days later joining the reconstituted 2nd Ohio Infantry as a corporal in Company G. Promoted to sergeant on March 13, 1862, Pittenger saw action in Andrews' Raid, also referred to as the Great Locomotive Chase.

Captured on April 15, 1862, near Lafayette, Georgia, he escaped execution as a spy and was imprisoned until March 18, 1863, when he was paroled via City Point, Virginia.

Following his release and subsequent receipt of the Medal of Honor, Pittenger was promoted to lieutenant and served until impaired health forced him to resign.

His official citation reads: "One of the 19 of 22 men (including 2 civilians) who, by direction of Gen. Mitchell (or Buell), penetrated nearly 200 miles south into enemy territory and captured a railroad train at Big Shanty, Ga., in an attempt to destroy the bridges and tract between Chattanooga and Atlanta.