Ernest Thornton was born in Waterford City, Ireland, on 17 March 1890, the son of Ernest I Thornton, an eminent local solicitor, of The Grange, Waterford.  He was educated privately by a governess before attending Cheltenham College between January 1901 and December 1904 when he joined the Royal Navy.

He served as a Midshipman in HMS SUFFOLK of the Third Cruiser Squadron in 1906, serving subsequently in HM Ships IRRESISTIBLE  and HINDUSTAN. He was promoted to Sub Lieutenant in July 1909 and to Lieutenant in April 1911, in which rank he served briefly in HMS INDOMITABLE.  In August 1911 He was appointed to HMS ARROGANT ‘…for a course of instruction in submarines’. He was serving in HMS A3 on 2 February 1912 having been appointed ‘as First Lieutenant’.

He is buried at Haslar cemetery and there is a plaque to his memory in Christ Church Cathedral, Waterford City.