During the Mexican–American War, he campaigned with Winfield Scott's army and received a brevet appointment as captain for gallantry at Contreras and Churubusco.

Named Chief of Artillery of Maj. Gen. Ambrose Burnside's IX Corps, he served at the battles of South Mountain and Antietam during the Maryland Campaign.

In March, 1863, Getty's division was sent to Suffolk, Virginia, where the Federal Army under Maj. Gen. John A. Dix successfully resisted Lt. Gen. James Longstreet's investment of the town, which guarded the southern approaches to Norfolk and Hampton Roads.

After subsequent engineering duty and command of a diversion to the South Anna River during the Gettysburg Campaign, Getty served as acting Inspector General of the Army of the Potomac.

In early 1864, Getty was assigned to command 2nd Division, VI Corps and fought with great bravery and determination to hold a vital road intersection at the Battle of the Wilderness on May 5–6, 1864.

He was wounded in the Battle of the Wilderness, but recovered to lead his troops during the lengthy Siege of Petersburg, and later in Maj. Gen. Philip Sheridan's Shenandoah Valley Campaign.

On December 12, 1864, President Abraham Lincoln nominated Getty for appointment to the brevet grade of major general of volunteers, to rank from August 1, 1864, confirmed by the U.S. Senate on February 14, 1865.

[1] Getty's division, including the famed Vermont Brigade, made the initial breakthrough at Petersburg on April 2, 1865, and took part in the final campaign of the Army of the Potomac, which concluded with the surrender of Robert E. Lee at Appomattox Court House.