Lord Harris attended the House of Lords throughout the war, where he championed county connections for the Volunteer units and fought for soldiers’ allowances. Outside of the House he raised funds for Kentish prisoners of war and arranged sports events.
In 1917 he was patron of a baseball game between the Canadians and Americans held at Lord’s, organised to raise funds for Canadian war widows and orphans. He also played there himself in 1918 for Pelham Warner’s XI against a Public Schools side, some fifty years after his first appearance at the Home of Cricket.
As Aide-de-Camp to the King, Lord Harris attended the monarch when he made troop inspections and did not relinquish his Commission until 1920, when he attained the age limit. He was a trustee of the Kent War Memorial Fund, which raised money to erect a memorial for the county at Canterbury. Lord Harris also unveiled the East Kent Yeomanry Memorial in Canterbury.