Medicinal plants provide a variety of secondary metabolites with varied chemical structures and biological activities. Among them, Allium sativum L. (garlic) is one of the most common edible and traditional plant that is used for the prevention and treatment of several diseases. A. sativum belongs to the family Liliaceae and it demonstrated diverse groups of natural compounds (185 compounds), such as organosulfur compounds, amino acids, selenium derivatives, saponins, phenyl propanoids, flavonoids, alkaloids, fatty acids, sterols and others. Therefore, this review focuses on the different classes of secondary metabolites that have been isolated from A. sativum, along with their valued pharmacological and therapeutic effects, e.g., anti-infective (antiprotozoal, antibacterial, antifungal and antiviral activities), antidiabetic, antihyperlipidemic, antihypertensive, heart protective, neuroprotective, hepatoprotective, antioxidant, anticancer, antiobesity, wound and scar healing, antianxiety, antidepressant, immunostimulant and memory enhancing properties. The potential of garlic in the treatment of many diseases such as gastrointestinal disorders, nephropathic encephalopathy and osteoarthritis has been also reported.