All life depends on redox chemistry. Concurrent oxidation and reduction reactions underpin many aspects of primary metabolism, from respiration to photosynthesis. But despite the evolution in nature of several systems that allow reduction and oxidation pathways to run concurrently, cyclic redox reaction networks have not been used to drive unidirectional motion in artificial molecular systems. In this paper we present a molecular motor in which autonomous unidirectional rotation about a C-C single bond is driven by a cyclic redox reaction network. Concurrent biocatalytic oxidation and chemical reduction reactions of a biphenyl motor create a cyclic reaction network that consumes fuel (oxygen and borane) to drive rotary motion about the biphenyl C-C bond, with directionality governed by the enantioselectivity of the oxidation biocatalyst. Isotopically labelled fuels and interrupted fuelling studies confirm the continuous operation of the rotary motor, and novel isotopomer methods confirm the directionality of rotation.