γ‐Lactones and their derivatives show diverse biological activities, and lactone skeletons are found in various naturally occurring products, pharmaceuticals, and agrochemicals. Although there are hundreds of methodologies for synthesizing γ‐lactone, the methods that are straightforward, environmentally friendly, and stereoselective are almost unknown. In this study, the molecular iodine/visible light‐mediated highly cis‐diastereoselective lactonization reaction of styrenes with Meldrum's acid was achieved. The developed reaction proceeded with the formation of a C−C bond at the olefin's β‐position and a C−O bond at its α‐position via a single‐step reaction with high diastereoselectivity and moderate‐to‐good yield.