Upon leaving school in 1894, Bentall joined the family drapery business in Kingston. By 1904 his father, Frank Bentall, had built a new department store on the site of the original firm where, within three years, they were selling china and glass, silver, beds, toys, and stationery. Leonard became general manager in 1909 when his father retired, and it was under his management that saw the conversion of Bentalls into a private limited company in 1925.
During the inter-war years Kingston as a town prospered, with the appeal of its shopping and entertainment districts leading to the slogan: "Why go to the West End -- when there's Bentalls of Kingston". This saw the continued expansion of Bentalls, with a new department store erected in the early 1930's. Leonard Bentall devoted a lot of time to his employees and their welfare, with a pension and bonus scheme both in place before the end of the 1920's. In his later life he was an avid cricketer, golfer, and gardener, and he created a magnificent garden at his home in Cobham where he lived with his wife Winifred.