This study aimed to investigate the plant growth-promoting and biocontrol potential of a grass culture with Paenibacillus ehimensis KWN8 on tomato. For this experiment, treatments of a chemical fertilizer (F), a bacterial grass culture (G), a 1/3 volume of G plus 2/3 F (GF), and F plus a synthetic fungicide (FSf) were applied to tomato leaves and roots. The result showed that the severity of Alternaria solani and Botrytis cinerea symptoms were significantly reduced after the application of the bacterial grass culture (G and GF) and FSf. In addition, root mortality in G and GF was lower compared to F. Tomato plants treated with G or GF had better vegetative growth and yield compared to F. Application of G affected the fungal and bacterial populations in the soil. In conclusion, treatment with a bacterial grass culture decreased disease severity and increased tomato growth parameters. However, there were no statistically significant correlations between disease occurrence and tomato yields. This experiment presents the possibility to manage diseases of tomato in an environmentally friendly manner and to also increase the yield of tomato by using a grass culture broth containing P. ehimensis KWN38.