In this study, a total of five plant-associated Proteus mirabilis were isolated from tomato (Lycopersicon esculentum Mill) plant and screened for plant growth-promoting (PGP) and antagonistic traits. The results revealed that all the isolates showed production of siderophore, and none of the isolates showed positive for hydrogen cyanide and lipase. Further, the antagonistic study of all isolates showed significant mycelial inhibition against Fusarium oxysporum. The isolate BETS2 showed best antagonistic activity against all phytopathogens tested in this study. The sequencing of 16S rRNA gene confirmed that all the isolates belong to the genus Proteus. The in vivo effect of BETS2 was demonstrated through tomato and chilli based bioassay under greenhouse conditions. The bacterial inoculation resulted in a significant increase in plant root, stem and plant biomass. The present study demonstrated that P. mirabilis could act as a plant growth-promoting bacterium.