Recently, tomatoes have been implicated as a primary vehicle in foodborne outbreaks of Salmonella Newport and other Salmonella serovars. Long-term intervention measures to reduce Salmonella prevalence on tomatoes remain elusive for growing and post-harvest environments. A naturally-occurring bacterium identified by 16S rDNA sequencing as Paenibacillus alvei was isolated epiphytically from plants native to the Virginia Eastern Shore tomato growing region. After initial antimicrobial activity screening against Salmonella and 10 other bacterial pathogens associated with the human food supply, strain TS-15 was further used to challenge an attenuated strain of S. Newport on inoculated fruits, leaves, and blossoms of tomato plants in an insect-screened high tunnel with a split-plot design. Survival of Salmonella after inoculation was measured for groups with and without the antagonist at days 0, 1, 2, 3, and 5 for blossoms and 6 for fruits and leaves, respectively. Strain TS-15 exhibited broad range antimicrobial activity against both major foodborne pathogens and major bacterial phytopathogens of tomato. After P. alvei strain TS-15 was applied onto the fruits, leaves, and blossoms of tomato plants, the concentration of S. Newport declined significantly (p≤0.05) compared with controls. The naturally-occurring antagonist strain TS-15 is highly effective in reducing carriage of Salmonella Newport on whole tomato plants. The application of P. alvei strain TS-15 is a promising approach for reducing the risk of Salmonella contamination during tomato production.