An effective anion sensor, [Ru^II(bpy)₂(H₂L⁻)]⁺ (1⁺), based on a redox and photoactive {Ru^II(bpy)₂} moiety and a new ligand (H₃L = 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid), has been developed for selective recognition of fluoride (F⁻) and acetate (OAc⁻) ions. Crystal structures of the free ligand, H₃L and [1](ClO₄) reveal the existence of strong intramolecular and intermolecular hydrogen bonding interactions. The structure of [1](ClO₄) shows that the benzimidazole N–H of H₂L⁻ is hydrogen bonded with the pendant carboxylate oxygen while the imidazole N–H remains free for possible hydrogen bonding interaction with the anions. The potential anion sensing features of 1⁺ have been studied by different experimental and theoretical (DFT) investigations using a wide variety of anions, such as F⁻, Cl⁻, Br⁻, I⁻, HSO₄⁻, H₂PO₄⁻, OAc⁻ and SCN⁻. Cyclic voltammetry and differential pulse voltammetry established that 1⁺ is an excellent electrochemical sensor for the selective recognition of F⁻ and OAc⁻ anions. 1⁺ is also found to be a selective colorimetric sensor for F⁻ or OAc⁻ anions where the MLCT band of the receptor at 498 nm is red shifted to 538 nm in the presence of one equivalent of F⁻ or OAc⁻ with a distinct change in colour from reddish-orange to pink. The binding constant between 1⁺ and F⁻ or OAc⁻ has been determined to be logK = 7.61 or 7.88, respectively, based on spectrophotometric titration in CH₃CN. The quenching of the emission band of 1⁺ at 716 nm (λ_ex = 440 nm, Φ = 0.01 at 298 K in CH₃CN) in the presence of one equivalent of F⁻ or OAc⁻, as well as two distinct lifetimes of the quenched and unquenched forms of the receptor 1⁺, makes it also a suitable fluorescence-based sensor. All the above experiments, in combination with ¹H NMR, suggest the formation of a 1 : 1 adduct between the receptor (1⁺) and the anion (F⁻ or OAc⁻). The formation of 1 : 1 adduct {[1⁺·F⁻] or [1⁺·OAc⁻]} has been further evidenced by in situ ESI-MS(+) in CH₃CN. Though the receptor, 1⁺, is comprised of two N–H protons associated with the coordinated H₂L⁻ ligand, only the free imidazole N–H proton participates in the hydrogen bonding interactions with the incoming anions, while the intramolecularly hydrogen bonded benzimidazole N–H proton remains intact as evidenced by the crystal structure of the final product (1). The hydrogen bond mediated anion sensing mechanism, over the direct deprotonation pathway, in 1⁺ has been further justified by a DFT study and subsequent NBO analysis.