Greenstreet was son of a Royal Artillery's Sergeant. He was educated at Southwark and he entered St John's College, Cambridge in 1879, graduating there in 1883. Then he was mathematics professor in different schools in Framlingham, East Riding and Cardiff before he became Head Master at Marling School in 1891. In 1910 he retired to Burghfield Common with the intention of devoting to literary work.[2]