Ag and Mn dopants were incorporated into Cu₂ZnSnS₄ thin film to reduce defects in thin film and improve thin film properties. Sol–gel and spin-coating techniques were employed to deposit Ag and Mn co-doped Cu₂ZnSnS₄ thin films. The structures, compositions, morphologies, and optical properties of the co-doped thin films were characterized. The experimental results indicate the formation of kesterite structure without Ag and Mn secondary phases. The amount of Ag in the thin films is close to that in the sols. The co-doped Cu₂ZnSnS₄ thin films have an absorption coefficient of larger than 1.3 × 10⁴ cm⁻¹, a direct optical band gap of 1.54–2.14 eV, and enhanced photoluminescence. The nonradiative recombination in Cu₂ZnSnS₄ thin film is reduced by Ag and Mn co-doping. The experimental results show that Ag and Mn incorporation can improve the properties of Cu₂ZnSnS₄ thin film.