The son of a grocer and master cheesemaker, Horatio Miller followed his father into the grocery trade. He was elected chief of the Leyton and Leytonstone Volunteer Fire Service in 1883 and led them to success in many competitions at home and abroad, including the silver medal at the 1900 Paris Olympics, when they finished second to Porto in the International Volunteer Firefighting competition. For his achievement as leader of the crew, Captain Miller was honoured with membership into the Federation of Sapeurs-Pompiers (Firefighters). In the 1890s, Miller was the chief local sanitary officer and inspector of nuisances for the Leytonstone area.