Soon after the outbreak of the Civil War, he enlisted April 16, 1861, as a private in the 49th Pennsylvania Infantry and was mustered in as the regiment's chaplain with the rank of captain.

He was elected chaplain of the National Military Home in Dayton, Ohio, on September 5, 1867, and held the post until illness forced him to retire.

[citation needed] Earnshaw was Commander of the Ohio Department, Grand Army of the Republic in 1876, Junior Vice-Commander in 1877, and presided at the national encampment of the G.A.R.

in Albany, New York, in 1879, when he was elected to serve as the national organization's 8th Commander-in-Chief.

[citation needed] He died July 7, 1885, in Dayton, Ohio, and is buried there in Woodland Cemetery and Arboretum.