Aging is a major global challenge, and there is growing demand for new strategies to address the burden of aging. The intensive search for antiaging agents has led to the discovery of a variety of drugs that promote the extension of healthspan and/or life. Metformin is a safe, effective, and globally affordable antihyperglycemic agent that has gained much attention in recent years as a potential antiaging treatment. Metformin has been shown to significantly delay the onset of age-related diseases and increase lifespan in several model organisms. In this paper, we reviewed aging hallmarks and the role of metformin in countering these hallmarks. We examined the beneficial effects of metformin on several age-related diseases and the feasibility of metformin as an agent to extend lifespan and healthspan. Finally, we discussed new research directions to better understand the translational potential of metformin in humans.