William was born in Canonbury, London, England to the Rev. Canon Harry Coate and Henrietta Mercy Nihill of The Vicarage, Sharnbrook, Bedfordshire. He was baptised on 7th Dec. 1889, at St. Andrew's Episcopal Church in Islington, London, England. William served as a captain in the 7th Battalion, Royal Munster Fusiliers and the 16th Battalion, Army Cyclist Corps, BEF. He was killed in action in Kakaraska, Macedonia, Greece. William's brother Alfred was killed a year later in France.