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An organic–inorganic cation–anion manganese(II) tetrabromide compound with diprotonated 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole, [H₃L][MnBr₄][H₂O], has been synthesized and investigated. The compound has a few possible pathways for proton transfers, which play an important role in the observed luminescence, optical, and magnetic properties. The proton transfers result in the appearance of two-band luminescence. One band is caused by the Mn(II) <i>d</i>-<i>d</i> transitions. The other band is caused by the transition from the triplet state of organic cation and the <i>d</i>-<i>d</i> transition of manganese(II) coupled through {[H₃L]}-{[MnBr₄]}-{[H₂O]} vibrations. The optical absorption spectra of [H₃L][MnBr₄][H₂O] indicate the presence of two direct and one indirect band transitions. The reason for the two-band luminescence and complex optical absorption in [H₃L][MnBr₄][H₂O] were additionally considered using the DFT calculations.