We present an approach allowing an optically pumped magnetometer (OPM) to be operated within the Earth’s magnetic field as a vector magnetometer, the sensitive axis of which can be freely defined. This approach enables the measurement of any vector component of the Earth’s magnetic field with the same sensitivity. The OPM is realized by a microfabricated cesium-vapor cell with nitrogen buffer gas, which is immersed in a constant homogeneous bias field of approximately 730 µT. Since this bias field is about one order of magnitude stronger than the Earth’s magnetic field, it defines the sensitive axis of the OPM. The bias field is generated by solid-state magnets and has been designed to exhibit a very low relative inhomogeneity ( 5 kHz. Our approach enables unshielded ultrasensitive vectorial measurement capabilities that are relevant in many important applications.