  A large-scale neutrino observatory based on Water-based Liquid Scintillator
(WbLS) will be excellently suited for a measurement of the Diffuse Supernova
Neutrino Background (DSNB). The WbLS technique offers high signal efficiency
and effective suppression of the otherwise overwhelming background from
neutral-current interactions of atmospheric neutrinos. To illustrate this, we
investigate the DSNB sensitivity for two configurations of the future Theia
detector by developing the expected signal and background rejection
efficiencies along a full analysis chain. Based on a statistical analysis of
the remaining signal and background rates, we find that a rather moderate
exposure of 190kt$\cdot$yrs will be sufficient to claim a ($5\sigma$) discovery
of the faint DSNB signal for standard model assumptions. We conclude that, in
comparison with other experimental techniques, WbLS offers the highest signal
efficiency of more than 80\% and best signal significance over background.
