Maize is an agro-economically important crop and its global scale cultivation dates back to ancient times. It is vital to find organic solutions for the agricultural sustainability of maize. Trichoderma spp. is a cheap bio-control candidate having favorable effects on plant growth and enhances resistance to abiotic stresses. Herein, the effect of the endophytic fungus Trichoderma atroviride, our local isolate named ID20G (TaID20G), was evaluated in maize (Zea mays L.) seedlings under drought stress. The fungal strain was characterized based on the internal transcribed spacer (ITS) sequence of 5.8S rDNA. Relative water content, phenotypic characters of roots, antioxidant enzyme activity, hydrogen peroxide content, lipid peroxidation and chlorophyll fluorescence (Fv/Fm ratio) were recorded. Root colonization of TaID20G increased fresh and dry weight of maize roots under drought stress. Chlorophyll and carotenoid contents of seedlings were reduced by drought stress and membrane damage was high in uninoculated plants. Root colonization of TaID20G almost totally prevented increase in lipid peroxidation and reversed the changes caused by drought in pigment contents and photosystem efficiency. Antioxidant enzyme activity was induced and hydrogen peroxide (H2O2) content was less in response to drought stress in inoculated plants. Taken together, these data indicate that TaID20G inoculation could diminish the injurious effects of drought and might have a function in arranging resilience against stress by inducing antioxidant machinery. Low cost and effortless nature of Trichoderma-based formulas might be developed as crop protectors in drought-affected lands around the world, leading to an eco-friendly insight into the plant stress tolerance.