Fowles was born in Leigh-on-Sea in Essex, England, the son of Gladys May Richards and Robert John Fowles. Robert Fowles came from a family of middle-class merchants of London. Robert's father Reginald was a partner of the firm Allen & Wright, a tobacco importer. Robert's mother died when he was six years old. At the age of 26, after receiving legal training, Robert enlisted in the Honourable Artillery Company and spent three years in the trenches of Flanders during the First World War. Robert's brother Jack died in the war, leaving a widow and three children. During 1920, the year Robert was demobilised, his father Reginald died. Robert became responsible for five young half-siblings as well as the children of his brother. Although he had hoped to practise law, the obligation of raising an extended family forced him into the family trade of tobacco importing.