This study aimed to comprehensively evaluate the potential health benefits of Thai basil extracts from two species, Ocimum basilicum var. thyrsiflorum and Ocimum basilicum cv. Jumbo 4320, by investigating their bioactivities, phytochemical composition, and in vitro antioxidant, antimicrobial, and antithrombotic activities. Thai basil extracts from two species (Ocimum basilicum var. thyrsiflorum and cv. Jumbo 4320) were obtained using water, ethanol, and ethyl acetate. Phytochemical analysis revealed chlorophylls, carotenoids, and diverse phenolic compounds. Its water extract boasted the highest total phenolics (459.62 ± 3.07 mg GAE/100 g), outperforming ethanol and ethyl acetate extracts (171.20 ± 1.10 and 66.02 ± 0.99 mg GAE/100 g, respectively). The ethanol extract of Jumbo 4320 also reigned supreme in total flavonoids (557.12 ± 14.27 mg CE/100 g), surpassing its counterparts (209.07 ± 23.31 and 131.41 ± 0.37 mg CE/100 g). O. basilicum cv. Jumbo 4320 extracts exhibited superior antioxidant activity by various assays. Jumbo 4320′s water extract further dominated in the DPPH assay (IC50 48.52 ± 1.15 mg/mL), demonstrating superior free radical scavenging compared to ethanol and ethyl acetate extracts (IC50 60.54 ± 0.52 and 82.09 ± 3.18 mg/mL), respectively. While thyrsiflorum’s ethanol extract claimed the top spot in the FRAP assay (0.0186 ± 0.00 mmol Fe2+/g), Jumbo 4320′s water extract showcased the highest cellular antioxidant activity (80.62 ± 0.00% relative fluorescence intensity) in the DCFH-DA assay. Interestingly, Ocimum basilicum var. thyrsiflorum extracts demonstrated stronger antithrombotic activity at prolonging the prothrombin time at 78.3 ± 17.56 s. While the antimicrobial activity against most tested pathogens was limited, both species’ extracts inhibited Bacillus cereus. These findings suggest the potential of Thai basil extracts, particularly from Jumbo 4320, as functional food ingredients with antioxidant and antithrombotic properties. © 2024 by the authors.