Microwave-metal (MW-metal) discharges can induce multiple effects, including heating, plasma, and light effects, which may open new pathways for enhancing chemical reactions via plasma-and photocatalysis. Heating and plasma effects have been researched extensively, with applications explored thoroughly. However, the photocatalytic effect of MW-metal discharges has been scarcely investigated. In this study, the photocatalytic effect of MW-metal discharges for the destruction of tar was investigated by comparing the conversion of a model tar compound under MW-metal discharges alone and under the synergetic effect of MW-metal discharges and a photocatalyst. Toluene was selected as the model tar compound, and anatase-type TiO2 was used as the photocatalyst. The experimental results show that anatase-type TiO2 can use the ultraviolet (UV) light emitted by MW-metal discharges to assist in the decomposition of toluene. Moreover, the discharge atmosphere plays an important role in discharge light characteristics. In comparison to pure nitrogen and pure argon atmospheres, the addition of a small amount of argon to nitrogen gas strengthens UV light emission. Correspondingly, the application of a photocatalyst enhanced toluene destruction efficiency when the carrier gas was a mixture of nitrogen and argon. The toluene conversion efficiency under the synergetic effect of MW-metal discharges and anatase-type TiO2 can amount to 98.4% when the N-2/Ar ratio was 5.