Practical photodynamic therapy calls for high-performance, less O₂-dependent, long-wavelength-light-activated photosensitizers to suit the hypoxic tumor microenvironment. Iridium-based photosensitizers exhibit excellent photocatalytic performance, but the in vivo applications are hindered by conventional O₂-dependent Type-II photochemistry and poor absorption. Herein, iridium complexes exhibiting Type-I photochemistry are screened and engineered to enhance absorption in the blue to NIR regions via a metallopolymerization strategy. Reactive oxygen species generation of metallopolymer Ir-P1, where the iridium atom is covalently coupled to the polymer backbone, is over 80 times higher than that of its mother polymer without iridium under 680 nm irradiation. This strategy also works effectively when the iridium atom is directly included (Ir-P2) in the polymer backbones, exhibiting its wide generality. The metallopolymer nanoparticles exhibiting efficient O₂^−• generation are further conjugated with integrin αvβ3 binding cRGD to achieve targeted PDT. This strategy is anticipated to provide general design guidelines for Type-I photosensitizers to meet practical requirements by judicious selection of metal complexes and organic building blocks.