Garran developed a strong relationship with Hughes, giving him legal advice on the World War I conscription plebiscites and on the range of regulations which were made under the War Precautions Act 1914. The War Precautions Regulations had a broad scope, and were generally supported by the High Court, which adopted a much more flexible approach to the reach of the Commonwealth's defence power during wartime. A substantial amount of Garran's work during the war involved preparing and carrying out the regulations.