The agricultural sector is a cornerstone of the national economy and faces significant challenges with key crops in Morocco, such as tomato. Establishing an ecological and sustainable cultivation system is therefore essential, including the use of alternatives to synthetic chemical inputs. This study evaluated the effects of Trichoderma asperellum, a beneficial fungus with biostimulant and bioprotective properties, on the growth and yield of greenhouse-grown tomato (Solanum lycopersicum). Four agronomic traits were assessed: fruit number, average fruit weight, yield per harvest, and shoot length. Application of T. asperellum enhanced all parameters, with effects depending on the applied concentration, plant developmental stage, and environmental conditions. A moderate volume of 5 L proved most effective during the active growth phase, producing 6.48 kg/m² and up to 57.71 fruits, while also promoting early development and activating plant defense mechanisms. Although overall performance declined by the end of the cycle, the 20 L volume maintained yield, highlighting the potential of T. asperellum to improve productivity throughout the growth cycle.