The technological appeal of multiferroics is the ability to control magnetism with electric field1-3. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroicmaterial exhibiting unambiguousmagnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetismarises fromthe canting of the antiferromagnetically aligned spins by the Dzyaloshinskii-Moriya (DM) interaction6-9. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of theDMvector by the ferroelectric polarization was forbidden10,11. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work10-12. Here we show a deterministic reversal of theDMvector and cantedmoment using an electric field at roomtemperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DMvector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching13,14.Given that theDMinteraction is fundamental to singlephasemultiferroics andmagnetoelectrics3,9, our results suggest ways to engineermagnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics. © 2014 Macmillan Publishers Limited.