A local isolate from root nodules of Acacia nilotica (L.), nitrogen fixing woody legume tree, grown in the Desert Garden, Aswan University Campus, Southeastern Desert, Aswan, Egypt, was carried out. A purified isolate was designated S-1T, was classified as Sinorhizobium saheli according to similarity and phylogenetic analysis of 16S rRNA., S-1T, is aerobic Gram-negative rod-shaped strain that was able to fix atmospheric nitrogen to produce NH3. S. saheli S-1T also showed capabilities to produce indole-acetic acid (IAA) and cellulase enzyme. S-1T, as a bio-fertilizer, was able to enhance Vicia faba growth under irradiance stress. Pot-culture experiments showed that strain S-1T increased the shoot and root length of V. faba by 27.0 and 27.1 cm, respectively, compared to inoculation-free control (negative control). Our findings highlight the role of S. saheli S-1T in improving plant growth of V. faba under irradiance stress through increasing chlorophyll and proteins content over control treatment and showing maximum photosynthesis rate (Pn) at high Photosynthetic Active Radiation levels (PAR). It was concluded that S. saheli S-1T possessed multiple beneficial effects for V. faba productivity when grown under extreme environmental conditions.