In 1927, Miller founded Miller Chevrolet Sales and Service in an Elkridge livery stable with 125 car sales his first year. He relocated to the Green-Cross Garage in Ellicott City in 1928. In 1938 the county closed many single-room schoolhouses and, using WPA money, built consolidated schools requiring bus service. Miller operated a school bus contracting service and serviced and exchanged vehicles for the county school system, the board of which he would become a member of. By 1968, he placed his son Paul as president and Donald as secretary of the auto dealership at a new location on Route 40. In 1972, he ended an eight-year service contract selling gas to Howard County's animal control vehicle fleet and driver's education cars.
