A micromechanical D'Arsonval magnetometer for sensing magnetic fields at low frequency with high sensitivity for operation near the resonant frequency of a micromechanical structure comprising a movable proof mass supported by torsion flexures, a conductive winding formed on the movable proof mass, at least one bridge electrode spanning the movable proof mass, a source for electrically biasing the movable proof mass relative to the bridge electrode(s), and a drive for electrically driving the conductive winding. Magnetic fields in the plane of the proof mass perpendicular to an axis of rotation formed by the torsion flexures interact with current passing through the conductive winding so as to torque the proof mass about the axis of rotation, whereby the resulting rotation is sensed through capacitors formed between the proof mass and the bridge electrode(s). The present invention micromechanical D'Arsonval magnetometer can be operated either open or closed loop. An open loop embodiment allows the proof mass to twist solely under the influence of the magnetic fields, while a closed loop embodiment restrains the proof mass motion. The loop can be closed by constructing additional electrodes or by using the existing bridge electrode(s) for both sensing and rebalancing.