Using vertex-corrected quasiparticle self-consistent GW schemes, we address the electronic structure of two manganese dioxide polymorphs, α-MnO2 and β-MnO2. In particular, we determine the fundamental band gaps, macroscopic dielectric constants, magnetic moments of the Mn atoms, band structures, and associated densities of states. Additionally, we obtain the imaginary component of the dielectric function ϵ2(ω) from the solution of the Bethe-Salpeter equation. For β-MnO2, we record overall good agreement when comparing the density of states with X-ray photoelectron spectroscopy and/or bremsstrahlung isochromat spectroscopy spectra and the dielectric function ϵ2(ω) with optical response spectra. Applied to α-MnO2, whose pristine bulk structure is poorly characterized, our work provides a prediction at the same level of theory. The quality of the achieved description is further supported by comparisons with experimental spectra of nanostructured and doped variants. This study demonstrates that state-of-the-art GW methods successfully account for key electronic-structure features of MnO2 polymorphs.