Aims Trichoderma harzianum is widely applied in agriculture as a biocontrol agent, biofertilizer, and biostimulant. This study aimed to isolate and characterize a Trichoderma harzianum strain from an arid agroecosystem and to evaluate its potential to promote plant growth across multiple crop species under stress-related and non-stressed conditions. Methods and results A fungal strain designated F115 was isolated from the rhizosphere of drought-cultivated millet in an arid region using the spread plate method and identified as Trichoderma harzianum based on morphological and phylogenetic analyses. Its plant growth-promoting potential was evaluated through pot experiments under drought- and salinity-stressed as well as non-stressed conditions. Strain F115 exhibited strong functional traits, including indole-3-acetic acid and siderophore production, phosphate solubilization, and antagonistic activity against Fusarium sp. and Alternaria sp., supported by the identification of corresponding biosynthetic genes in its draft genome. Inoculation with F115 significantly increased root and shoot biomass and stem diameter in five crops-millet, oat, sunflower, pepper, and pumpkin-resulting in a significantly higher Dickson Quality Index (DQI) (P < 0.05). These growth responses were positively associated with enhanced plant enzyme activities, improved soil nutrient availability, increased rhizospheric enzyme activities, and elevated abundances of total bacteria, fungi, and nitrogen-fixing bacteria. Conclusion Trichoderma harzianum F115 exhibits notable biocontrol potential and biostimulation abilities, along with adaptability to multiple plant hosts and stress-related conditions.