He was born at Teddington, the son of Alfred Hills Stoner and Sarah Louise Stoner, and educated at Kingston Grammar School. His father and grandfather were quantity surveyors, and he was trained in this profession at the offices of the family firm in Broad Street, City of London. As soon as he was 21, he took up writing as a career in the Literary London of the 1920s, though he later put his surveying to good use in wartime.
He used the nom-de-plume Oliver Stonor because he felt it looked and sounded better than his own name; the "er" at the end of "Oliver", clashing with "Stoner", prompted the change to "Stonor". He was not related to the Stonor family of Stonor Park; the Stoners came originally from Cowfold in Sussex; his grandfather had bought Harcourt, near Pembury, in Kent. The name Morchard Bishop is actually that of a town in Devon.
In 1926, he visited the home of the writer Arthur Machen, who was living at Melina Place. He joined the wide and varied circle of those who sought out and admired Machen for his conversation, as well as for his writing; and when Machen and his wife Purefoy moved to Amersham, they stayed in touch.