Plants are vital in maintaining the food chain and have a significant impact on surrounding microbes due to the presence of allelochemicals. The potential allelopathic effects of java plum plant parts were assessed on seed germination and seedling growth of soybean, cucumber, carrot, rice, wheat, and maize. The results indicated that S. cumini significantly retarded the germination of soybean, cucumber, and rice while stimulating carrot germination. S. cumini had a diverse effect on the seedling growth of soybean, rice, and carrot, with an inhibitory effect on carrot growth. Significant reduction in radicle and hypocotyl growth of soybean and rice was observed. Aqueous extracts of S. cumini plant parts were also tested for antibacterial activity against Escherichia coli and Acinetobacter baumannii and antifungal activity against Aspergillus niger and Candida albicans. Stem, seed, and fruit extracts of S. cumini inhibited the growth of A. baumannii at the highest concentration, while leaf extract inhibited the growth of E. coli. Stem and fruit extracts had negative effects on the growth of A. niger. Knowing the significant allelopathic and antimicrobial potential of S. cumini, further studies on its allelochemicals can help in using this plant species for agricultural and medicinal purposes.