Dickinson was born in London, the son of Lowes Cato Dickinson (1819–1908), a portrait painter, by his marriage to Margaret Ellen Williams, a daughter of William Smith Williams who was literary advisor to Smith, Elder & Company and had discovered Charlotte Brontë. When the boy was about one year old his family moved to the Spring Cottage in Hanwell, then a country village. The family also included his brother, Arthur, three years older, an older sister, May, and two younger sisters, Hester and Janet.