Introduction: Garlic (Allium sativum) is a popular food spice worldwide with many health benefits. Garlic and its products have been used to treat various infections in traditional medicine in India, the Middle East, and Southeast Asia. Garlic and its organosulphur compounds have antibacterial properties against methicillin-resistant Staphylococcus aureus (MRSA), but the antibiofilm property and interaction with methicillin have been relatively unexplored. Biofilm formation is crucial in MRSA infections, one of the most common nosocomial infections. Method: The antibacterial activity fresh garlic extract (FGE) against MRSA was evaluated by determining the minimum inhibitory concentration (MIC) and zone of inhibition using microdilution and well diffusion assays respectively. Microtiter plate crystal violet assay and scanning electron microscopy was use to evaluate the antibiofilm activity of FGE against MRSA. Results: Sub-MIC concentrations of FGE significantly reduce methicillin-susceptible S. aureus (MSSA) and MRSA biofilm formation. Scanning electron microscopy analysis suggests that FGE reduces the attachment of MSSA and MRSA. Diallyl sulphide, one of the organosulphur compounds of garlic, inhibited the biofilm formation of MSSA and MRSA. Sub-MIC concentration of FGE also sensitized MRSA to methicillin, completely inhibiting MRSA growth when used in combination. Similar effects were noticed when FGE was combined with other β-lactam antibiotics to which MRSA was resistant. Conclusions: The study validates garlic as an antibacterial agent in ethnomedicine through scientific evidence. Garlic and its organosulphur compounds are potential antibiofilm agents against MRSA. Moreover, garlic could be potentially used as a complementary or alternative medicine to treat infections caused by drug-resistant bacteria such as MRSA.