With increasing meat demand and global warming, the sustainability of broiler chicken production has become a “hot topic” for the conventional industry. We conducted a life cycle assessment (LCA) to compare the environmental impact of supplementing broiler chicken diets with postbiotics derived from the yeast cell wall (YCW). Supplementation with S. cerevisiae reduced the carbon footprint of climate change (8.4%), land use (8.7%), water use (7.7%), resource use (7.9%), acidification (12.5%), marine eutrophication (9.5%), freshwater eutrophication (8.6%), terrestrial eutrophication (12.6%), and particulate matter (11.4%). The positive effects on the environmental impact were associated with improvement in the feed conversion ratio (FCR: −7.6%), body weight gain (BWG: +5.7%) and a reduction in mortality of around 44.1%. Overall, the environmental benefit was similar in chickens exposed to heat stress (−8.7%) or challenged with Clostridium perfringens (−8.2%), two stressful situations commonly encountered on poultry farms. This LCA study demonstrates that S. cerevisiae is a food additive that can help the poultry industry cope with stress caused by various factors and reduce its overall environmental impact.