Background: Early blight disease of tomato caused by pathogenic fungi Alternaria solani is the most significant and common disease throughout the world as well as in Kingdom of Saudi Arabia. The aim of this study was to isolate and identify native Trichoderma species from the Jeddah region in Saudi Arabia; evaluate their antagonistic potential against A. solani; and study their influence early blight disease severity in greenhouse and in open field. Results: The present study focused to explore the biocontrolling potential of native Trichoderma spp. against A. solani strain to compare with a conventional fungicide. Out of 21, 3 Trichoderma isolates showed an antifungal activity and significantly inhibited the mycelial growth of pathogen that were identified as Trichoderma atroviride, T. harzianum and T. longibrachiatum by their ITS region sequence analysis. Strong in vitro mycelial growth suppression (70.66%) was also recorded at 400 ppm Mancozeb (90%WP®) fungicide. Further, these Trichoderma bioagents and fungicide were further evaluated in greenhouse (artificially inoculated) and in field on naturally infected tomato plants. In greenhouse, (13.74%) disease severity after T. harzianum treatment was recorded, followed by T. longibrachiatum (25.83%) and T. atroviride (21.67%). The disease severity after fungicide (50 mg/L; 10 ml per plant) application was (7.91%). Further, positive impact on the plant biomarkers was demonstrated by all selected Trichoderma isolates in greenhouse. Under natural infection in season I, the disease severity (%) after T. longibrachiatum, T. atroviride and T. harzianum treatments was 11.5, 13.26 and 16.81%, respectively, followed by control (32.12%), whereas 7.18% disease severity was recorded after fungicide application. Conclusions: The results revealed that native Trichoderma of this region had potential to mitigate the early blight disease intensity in field.