Abiotic stresses negatively affect the rate of nutrient mobilization in soils resulting in poor crop performance. Vermicompost-leachate (VCL) is an organic liquid produced from earthworm-digested material. It improves soil fertility as a result of the presence of proteins, vitamins, and micro- and macroelements. However, the effects of VCL on plant growth under temperature and water stress are not yet fully studied. To assess the growth performance under low, optimum, and high temperatures, 1-month-old well established tomato seedlings were treated with and without VCL (1:10 v/v) under various temperature regimes (10, 15, 20, 25, and 30 °C). In the second trial, tomato seedlings were tested in a greenhouse with and without VCL (1:10 v/v) at different watering regimes (15, 30, and 45 mL of Hoagland’s nutrient solution) to evaluate the effect of water stress. In comparison with the control seedlings, VCL treatment significantly improved stem thickness, leaf area, and shoot/root both fresh and dry weight of seedlings at 30 °C. At this temperature, VCL-treated seedlings showed a significant increase for all examined physiological parameters (total chlorophyll, total sugars, and proline). Number of leaves, stem thickness, and shoot/root length and fresh weight of VCL-treated tomato seedlings irrigated under a low watering regime were significantly greater than the control. Total chlorophyll, total sugars, and proline content were significantly elevated at the high watering regime but declined in the low watering regime with VCL treatment. Both increasing and decreasing trends of compatible solutes and photosynthetic pigments indicated osmotic adjustment to stress conditions. VCL can be a suitable soil amendment product to improve overall soil fertility and, more importantly, growth of tomato plants even under temperature and water stress conditions.