An electric motor system includes an electric motor, and a thermal management system. The thermal management system includes a two-phase refrigerant circuit circulating a flow of refrigerant through the electric motor, and a refrigerant-air heat exchanger fluidly connected to the electric motor via the two-phase refrigerant circuit, such that the flow of refrigerant is boiled via heat generated by the electric motor, and returned to a subcooled liquid state to cool the electric motor. A method of dissipating thermal energy from an electric motor includes urging a flow of refrigerant through an electric motor, thereby boiling the flow of refrigerant, directing the flow of refrigerant from the electric motor to a refrigerant-air heat exchanger via a two-phase refrigerant circuit, and cooling the refrigerant to a sub-cooled liquid state at the refrigerant-air heat exchanger via thermal energy exchange with a flow of air through the refrigerant-air heat exchanger.