He was born at Weybridge, the eldest son of Henry Gay Hewlett, of Shaw Hall, Addington, Kent. He was educated at the London International College, Spring Grove, Isleworth, and was called to the bar in 1891. He gave up the law after the success of The Forest Lovers. From 1896 to 1901 he was Keeper of Lands, Revenues, Records and Enrolments, a government post as adviser on matters of medieval law.
Hewlett married Hilda Beatrice Herbert on 3 January 1888 in St Peter's Church, Vauxhall, where her father was the incumbent vicar. The couple had two children, a daughter, Pia, and a son, Francis, but separated in 1914, partly due to Hilda's increasing interest in aviation. In 1911, Hilda had become the first woman in the UK to gain a pilot's licence.[2]
Hewlett's 1900 novel The Life and Death of Richard Yea-and-Nay, about Richard the Lionheart, was a favourite novel of T. E. Lawrence. Lawrence said he had read The Life and Death of Richard Yea-and-Nay several times.[3] Another of Hewlett's historical novels was The Queen's Quair (1904), about Mary, Queen of Scots. The Queen's Quair was cited as an influence by Ford Madox Ford, who said that The Queen's Quair "taught me a good deal".[4] Hewlett also wrote six novels based on the Icelandic Family sagas, these include The Light Heart and Thorgils of Treadholt. Hewlett also wrote The Outlaw (based on Gisli's Saga), A Lover's Tale (based on Kormak's Saga), Frey and His Wife (based on Ogmund Dytt's tale), and Gudred the Fair (based on the Greenland sagas).[5]
This list omits some significant works. He wrote six novels based on the Icelandic Family sagas, of which only The Light Heart and Thorgils of Treadholt are mentioned above. There is also The Outlaw (based on Gisli's Saga), A Lover's Tale (based on Kormak's Saga), Frey and His Wife (based on Ogmund Dytt's tale), and Gudred the Fair (based on the Greenland sagas).