In-situ high-energy synchrotron X-ray diffraction experiments during uniaxial tensile loading are performed to investigate the effect of temperature (25, 45 and 70 degrees C) on the deformation behavior of a 301 metastable austenitic stainless steel. The micromechanical behavior of the steel at the three deformation temperatures is correlated with the stacking fault energy (gamma(SF)) experimentally determined through the same in-situ X-ray experiments. The applied measurements provide a unique possibility to directly interrogate the temperature dependent gamma(SF) in relation to the active bulk deformation mechanism in a metastable austenitic stainless steel. The determined gamma(SF) is 9.4 +/- 1.7 mJ m(-2) at 25 degrees C, 13.4 +/- 1.9 mJ m(-2) at 45 degrees C and 25.0 +/- 1.1 mJ m(-2) at 70 degrees C. This relatively minor change of gamma(SF) and temperature causes a significant change of the dominant deformation mechanism in the alloy. At room temperature (25 degrees C) significant amounts of stacking faults form at 0.05 true strain, with subsequent formation of large fractions of deformation-induced alpha' and epsilon-martensite, 0.4 and 0.05, at 0.4 true strain, respectively. With increasing temperature (45 degrees C) fewer stacking faults form at low strain and thereupon also smaller alpha' - and epsilon-martensite fractions form, 0.2 and 0.025, at 0.4 true strain, respectively. At the highest temperature (70 degrees C) plastic deformation primarily occurs by the generation and glide of perfect dislocations at low strain, while at higher strain these dislocations dissociate to form stacking faults. The alpha'-martensite fraction formed is significantly less at 70 degrees C reaching 0.1 at 0.4 strain, whilst epsilon-martensite is not found to form at any strain at this temperature. The temperature-dependent mechanical behavior of the alloy is consistent with the observed dominant deformation mechanisms; the strong work hardening from the TRIP effect at low temperature, and low gamma(SF), decreases significantly with increasing temperature, and gamma(SF).