Ambient methane detection remains constrained by humidity interference and insufficient sensitivity at room temperature. Compared with standalone Ti₃C₂T_x MXene, hetero-structured ZnO-pillared Ti₃C₂T_x MXene was engineered via a simple self-assembly method at room temperature, achieving breakthrough room-temperature moisture-tolerant CH₄ sensing at ppm level (< 1 ppm detection limit, response of 21.3% to 100 ppm CH₄ at 80% relative humidity (RH). Through in-situ electronic paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) spectroscopy, we demonstrate visible-light-driven hydroxyl radical (·OH) generation at ZnO/MXene interfaces in humid conditions. These radicals activate the catalytic conversion from CH₄ to CO₂ at reduced energy barriers, overcoming humidity poisoning by preferential H₂O dissociation, enhancing the sensing performance together with the increased hole concentration and the improved activity of oxygen species. This study not only paves a new way for designing MXene-based gas sensors adaptable to diverse environmental conditions, but also establishes a hetero-engineering paradigm for radical-mediated gas detection.