In vitro and in vivo studies were carried out to evaluate aqueous extracts from Allium sativum L. (Garlic) against Ralstonia solanacearum isolated from an infected tomato plant. Four concentrations, (10, 20, 30 and 40%) of aqueous garlic extracts were prepared using cool (35o C) and hot (70o C) water. Evaluation of the extract concentrations against the pathogen was done using the agar well diffusion method in a nutrient agar medium. Incubation was for 48 hours at 35o C. In the in vivo studies, the most effective concentrations of garlic extracts were used as seed priming agents on tomato seeds sown in R. solanacearum infested soil in plastic pots. All data collected were subjected to statistical analysis using Minitab software (Version 17), while means were separated using Tukey’s test. Results showed that cool garlic extracts at 40% had a 30.63 mm zone of inhibition against the pathogen. This was significantly higher than 10.90 mm recorded by 10% of both cool and hot extracts. Hot extract, 40%, treated seeds recorded the highest number of leaves (21.75), had no incidence of bacterial wilt, gave the best plant height (45.75 cm) and fruit weight (327.1 g), surpassed only by the standard check. There is a need for more work to be done to developing an antibacterial agent from garlic for the management of bacterial wilt disease of tomatoes.