Trichoderma-based biostimulants are considered the most effective plant growth–promoting fungi. The purpose of this study is to determine the effect of two Trichoderma saturnisporum isolates on the growth promotion of melon (Cucumis melo) seeds and seedlings as well as their effect on the performance of the cantaloupe “Charentais” melon crop cultivar Gandalf cultivated under a typical parral-type greenhouse. For these purposes, germination trials and two experiments were performed in a commercial nursery, conventional system, and large plant system. Two experiments were also established for 2 years (two crop cycles) in a commercial greenhouse in Almería, Spain. In addition, we evaluated the influence of these isolates (T1 and T2) on the Charentais melon yield and quality. High values for seedling vigor and root length were obtained by T. saturnisporum T1 (93.50%) and T2 (93.75%) against control (62%). Trichoderma saturnisporum T1 and T2 increased the quality of plants in conventional system and large plant system and can be considered as biostimulant. Trichoderma saturnisporum treatments resulted in significantly larger crop productivity without a negative effect on the fruit quality parameters. Melon productivity increased in T. saturnisporum treatments T1 (13.99%) and T2 (16.04%), while at the same time increases the average fruit weight up to 7.71% for T2 isolate. Trichoderma saturnisporum act as biostimulants for nursing and commercial melon crops without negative effects on fruit quality. This is the first report describing T. saturnisporum as a potential crop yield promoter.