The diffuse supernova neutrino background (DSNB) is the constant flux of neutrinos and antineutrinos emitted by all past core collapses in the observable Universe. We study the potential to extract information on the neutrino lifetime from the upcoming observation of the DSNB flux. The DSNB flux has a unique sensitivity to neutrino nonradiative decay for $\tau / m \in \left[ 10^9, 10^{11}\right]$ s/eV. To this end, we integrate, for the first time, astrophysical uncertainties, the contribution from failed supernovae, and a three-neutrino description of neutrino nonradiative decay. We present our predictions for future detection at the running Super-Kamiokande + Gd and the upcoming Hyper-Kamiokande, JUNO, and DUNE experiments. Finally, our results show the importance of identifying the neutrino mass ordering to restrict the possible decay scenarios for the impact of nonradiative neutrino decay on the DSNB.