Doping a foreign atom to metal oxides enables the modulations of the electronic and chemical properties of active sites. SnO2 quantum wires (QWs) possessing large surface area with highly exposed active sites have been demonstrated as promising sensing materials in gas sensors but they still suffer from the unsatisfactory selectivity and limit of detections (LODs). Herein, we realize the electronic interaction of transition metal atoms (Cr, Mo, and W) and sub-3 nm ultrathin SnO2 QWs using a general one-step solution process at low temperature (180 °C). Density functional theory calculations reveal that such tailored electronic structures reduce energy barriers for adsorption of gas molecules and transportation of electrons, which facilitates oxygen adsorption and activation, and thus accelerates surface reaction kinetics with H2S molecules. Our results indicate that the transition metal doping induces more oxygen vacancies (VO) that lead to boosted H2S chemical-sensing performances. A representative W-doped SnO2 QWs (W-SnO2) achieve enhanced low-temperature H2S-sensing properties with a record LOD of down to 0.48 ppb, which surpasses most of the reported metal oxide-based gas sensors.