The Duplex Motorcar Company was established in Chicago, Illinois, and operated from 1908 to 1909. The company produced automobiles characterized by their unique high-wheeler design, which featured a transverse-mounted 2-cylinder engine. This innovative configuration included two friction discs located at each end of the crankshaft, with separate propeller shafts driving a differential on the rear axle. This mechanical setup bore similarities to that of the DUMONT vehicle.

In its inaugural year, 1908, Duplex offered three models, including Stanhopes equipped with either 10 or 15 horsepower engines, as well as a surrey model. By 1909, the company transitioned to a more conventional design, introducing a vehicle with standard-sized wheels, a prominent bonnet, and a four-seater body. The Duplex Motorcar Company was a subsidiary of the Bendix Company, which also manufactured vehicles under its own brand name.