There is limited information about the importance of seed origin, thermoperiod, and photoperiod on low water potential tolerance during seed germination of habitat-indifferent plants, which grow well in saline and non-saline habitats. This study examined the effects of seed provenance, water potential, thermoperiod, photoperiod, and their interactions on seed germination of the multipurpose exotic tree Prosopis juliflora. Seeds from saline and non-saline habitats were germinated under various water potential levels at different thermoperiods and photoperiods. Seeds could endure up to −1.5 MPa water potential irrespective of origin. Germination of seeds from saline habitats was higher than those from non-saline habitats in −1.5 MPa. At 0 and -0.3 MPa, seeds germinated in a thermoperiod-insensitive manner in light. At < -0.6 MPa, however, a higher thermoperiod was more inhibitory for germination. Seeds germinated better under dark than light conditions under low water potential and high thermoperiod. Most ungerminated seeds from different lower water potential treatments recovered their germination when transferred to distilled water. This study demonstrated that the low water potential tolerance of P. juliflora seeds depends on seed origin, thermoperiod, and photoperiod. These factors should be considered when selecting a seed lot for afforestation of P. juliflora in different soil types.