Returning to his regiment he participated in the campaigns against the Indians in Oregon and Washington Territory, and was an aide to Brig.

[1] Promoted to captain, he was serving as Adjutant General of the Department of Oregon when the American Civil War began.

Franklin did not conduct his attack to Maj. Gen. Ambrose E. Burnside's expectations, and Hardie has been criticized for not ensuring that the two generals understood each other correctly.

On June 28, 1863, Hardie was the officer who delivered the surprise order to Maj. Gen. George G. Meade at Frederick, Maryland, appointing him commander of the Army of the Potomac, three days prior to the Battle of Gettysburg.

In 1876 he was elected as a Companion of the Pennsylvania Commandery of the Military Order of the Loyal Legion of the United States.