 Clarke entered the Royal Engineers in 1868, served in the Egyptian Expedition and as Assistant Political officer during the following Sudan expedition.From 1885 until 1892 Clarke was secretary to the Colonial Defence Committee, for which he was knighted as a Knight Commander of the Order of St Michael and St George (KCMG) in 1893.He was also secretary to the Royal Commission on Navy and Army Administration in 1888, a commission which did much to improve cooperation between the two services.