By immobilizing a B12 complex and a Ru(ii) trisbipyridine photosensitizer in a polymerized ionic liquid (PIL), a visible light-driven photocatalyst was developed. The synthesized copolymer was characterized by GPC and DLS, and using UV-vis absorption spectra and luminescence spectra. The Ru(ii) trisbipyridine photosensitizer in the copolymer showed an enhanced emission compared to that of the monomer in the ionic liquid, 1-butyl-4-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][NTf2]). Formation of the Co(i) species of the B12 complex in the copolymer was confirmed by the UV-vis spectral change in [C4mim][NTf2] containing a sacrificial reductant (triethanolamine) under irradiation with visible light. The copolymer showed a high photocatalytic activity in various ionic liquids for 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) dechlorination with ∼99% conversion after visible light irradiation for 2 h. Furthermore, both the B12 catalyst and photosensitizer in the polymer were easily recycled for use with the ionic liquid solvent without any loss of catalytic activity.