Harry W. Arnold was born on December 19, 1855 in Norristown, Pennsylvania.

His father, George W., served in the 4th Regiment Pennsylvania Infantry and the 51st Regiment Pennsylvania Infantry from April 20, 1861 to September 27, 1963. He enlisted as a private and mustered out as a sergeant.

Harry joined the Sons of Veterans in October 6, 1883 with the Speer Orr Camp 14, Johnstown, Pennsylvania and became its first Captain. He was elected to Colonel of the West Pennsylvania Division on March 14, 1884.

At the 1884 National Encampment the following were nominated for Commander-in-Chief: E. W. Alexander (PA), G. W. Penniman (MN), and H. W. Arnold (PA). Alexander received 10 votes, Arnold had 10, and Penniman had 18. There wasn't a majority and Alexander had his name withdrawn. With the second ballot, Arnold received 20 votes and Penniman had 18. On a motion by J. B. Maccabe, the election of Arnold was made unanimous and the motion carried.

In the Spring of 1886, health difficulties warranted his move to Denver, Colorado. He return back to Johnstown on October 1, 1887.

Harry never married and had no children.

Brother Arnold died, caused by his pulmonary disease, on January 12, 1889 in Johnstown. He is buried in Grandview Cemetery in Southmont, Pennsylvania. He was the first Past Commander-in-Chief to die. At the 1889 National Encampment a motion was made and carried to donate $100 for placing a suitable headstone or other monument at his grave.