Soil salinity and lead (Pb) toxicity severely degrade soil health and crop productivity in arid regions. This study investigated the combined use of deashed biochar (DAB) and compost (COM) to alleviate salinity stress (SS) and Pb stress (LS) in lettuce under greenhouse pot experiment where crop physiological traits, oxidative stress responses, and soil-plant nutrient interactions were analyzed. Co-application of DAB+COM increased total chlorophyll (32.29%), photosynthetic rate (18.49%), transpiration rate (17.82%), and stomatal conductance (55.24%) under SS, with comparable enhancements under LS. Moreover, stress-induced markers like electrolyte leakage, carotenoids, and proline contents declined by 21.83%, 28.76%, and 24.73% in SS, whilst at LS these contents dropped to 19.13%, 23.94%, and 24.56%, respectively. Antioxidant enzyme activities (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, glutathione reductase) in roots and leaves were substantially reduced in DAB+COM treatment under both stresses. Pb accumulation decreased by 20.68% (roots) and 17.61% (leaves), whilst soil N, P, and K availability improved substantially under DAB+COM amendments. Overall, these results suggest that synergistic amendment of DAB+COM offers a sustainable approach to rehabilitate degraded soils and enhance crop resilience in arid agroecosystems.