Achieving high-performance, low-power gas detection at room temperature is critical to safety and energy efficiency, and the key is to deeply explore the interaction mechanisms between sensitive materials and gases. In this work, a magnetic field-assisted strategy is developed to achieve high-performance, low-power NO₂ sensing with the Fe₃GaTe₂ at room temperature. Fe₃GaTe₂ nanoflakes are obtained from green solvents using ultrasound-assisted liquid phase exfoliation. The experimental results confirming that the Fe₃GaTe₂ nanoflakes sensor demonstrates an excellent response (S = 16 for 10 ppm NO₂, 1.4 times higher than that without magnetic field), a lower actual detection limit (50 ppb) and a low-power consumption (0.25 nW) under 21 mT magnetic field at room temperature. Combining theoretical calculations and quasi in situ XPS, it is indicated that Fe is the main electron donor and serves as the main response site for NO₂. Magnetic field-enhancing effect for gas sensing is revealed via comparing the in situ field-dependent magnetization curves of Fe₃GaTe₂ in air and NO₂. It is found for the first time that the enhancement of gas sensing is mainly attributed to the gas adsorption magnetic variation effect (GAMVE) which generates in NO₂. This study provides a strategy of GAMVE-driven sensing for next-generation gas sensors.