Harold was the son of George Thomas and Ellen Maria Horsley who lived at 94 Sidney Grove, Newcastle upon Tyne. He had nine siblings: Margaret Ann, Thomas William, Ellen Frances, George E, Edward C, Sidney G, Edith J, Arthur, and Mabel Elizabeth.
He attended Armstrong College as a corporation scholar, and studied mathematics, and engineering, gaining a BSc. Before the war, Harold was an Apprentice Ships’ Draughtsman.
Harold was killed in action on 1st October 1916 aged 27. This was the first day of the Battle of Le Transloy phase of the Somme. It was a period of fighting in terrible weather which became as formidable as the German enemy. In this battle, the British gradually pressed forward, fighting against numerous counter-attacks, in an effort to have the front line on higher ground from which the offensive could be renewed in 1917.