A promising route to widespread deployment of photovoltaics is to harness inexpensive yet high-efficiency tandems. Perovskites are one of the most promising technologies to facilitate such a concept. Here we perform holistic analyses, from a life-cycle assessment perspective, on the energy payback time, greenhouse gas emission factor, and environmental impact scores for perovskite-silicon and perovskite-perovskite tandems benchmarked against state-of-the-art commercial silicon cells. The scalability of processing steps and materials, along with the uncertainty in the manufacture and operation of tandems, are explicitly considered to ensure realistic estimates of values. Notably, the resulting energy payback time and greenhouse gas emission factor of the all-perovskite tandem configuration are as low as 0.35 years and 10.7 g CO2-eq/kWh, respectively, compared to 1.52 years and 24.6 g CO2-eq/kWh for the silicon benchmark. Both tandem architectures demonstrate a substantial reduction in payback period by virtue of perovskites compared to silicon photovoltaics, but the greenhouse gas emission factors of the perovskite-silicon tandem are still dominated by silicon. Prolonging the lifetime provides a strong technological lever for bringing down the greenhouse gas emission factor such that even the perovskite-silicon tandem can outcompete the current benchmark on environmental factors as well as power and cost performance. Perovskite-perovskite tandems with flexible and lightweight form factors further cut these numbers down to 0.33 years and 10.0 g CO2-eq/kWh, and thus enhance the potential for large-scale, sustainable deployment.